A tree structure (i.e. a rooted, connected acyclic graph) is often used in programming.

It's often helpful to visually examine such a structure.

There are many ways to represent trees to a reader, such as:

indented text (à la unix tree command)
nested HTML tables
hierarchical GUI widgets
2D or 3D images
etc.

Task

Write a program to produce a visual representation of some tree.

The content of the tree doesn't matter, nor does the output format, the only requirement being that the output is human friendly.

Make do with the vague term "friendly" the best you can.

11l

Translation of: D

<lang 11l>T Node

  String value
  Node? left
  Node? right

  F (value, Node? left = N, Node? right = N)
     .value = String(value)
     .left = left
     .right = right

  F tree_indent() -> [String]
     V tr = I .right != N {.right.tree_indent()} E [‘-- (null)’]
     R [‘--’(.value)] [+] (I .left != N {.left.tree_indent()} E [‘-- (null)’]).map(a -> ‘  |’a)
                      [+] [‘  `’tr[0]] + tr[1..].map(a -> ‘   ’a)

V tree = Node(1, Node(2, Node(4, Node(7)), Node(5)), Node(3, Node(6, Node(8), Node(9)))) print(tree.tree_indent().join("\n"))</lang>

Ada

Prints a tree of the current directory. <lang Ada>with Ada.Text_IO, Ada.Directories;

procedure Directory_Tree is

  procedure Print_Tree(Current: String; Indention: Natural := 0) is
     
     function Spaces(N: Natural) return String is

(if N= 0 then "" else " " & Spaces(N-1));

     use Ada.Directories;
     Search: Search_Type;
     Found: Directory_Entry_Type;
     
  begin
     Start_Search(Search, Current, "");
     while More_Entries(Search) loop

Get_Next_Entry(Search, Found); declare Name: String := Simple_Name(Found); Dir: Boolean := Kind(Found) = Directory; begin if Name(Name'First) /= '.' then

              -- skip all files who's names start with ".", namely "." and ".."

Ada.Text_IO.Put_Line(Spaces(2*Indention) & Simple_Name(Found) & (if Dir then " (dir)" else "")); if Dir then Print_Tree(Full_Name(Found), Indention + 1); end if; end if; end;

    end loop;
  end Print_Tree;

begin

  Print_Tree(Ada.Directories.Current_Directory);

end Directory_Tree;</lang>

Output:

outer (dir)
  inner (dir)
    innermost (dir)
      file
      another
file
some

ALGOL 68

<lang algol68># outputs nested html tables to visualise a tree #

mode representing nodes of the tree #

MODE NODE = STRUCT( STRING value, REF NODE child, REF NODE sibling ); REF NODE nil node = NIL;

tags etc. #

STRING table = "

" , elbat = "

" , tr = "" , rt = "" , td = "<td style=""text-align: center; vertical-align: top; """ , dt = "" , nbsp = " " ; CHAR nl = REPR 10;

returns the number of child elements of tree #

OP CHILDCOUNT = ( REF NODE tree )INT: BEGIN INT result := 0; REF NODE child := child OF tree; WHILE REF NODE( child ) ISNT nil node DO result +:= 1; child := sibling OF child OD; result END # CHILDCOUNT # ;

generates nested HTML tables from the tree #

OP TOHTML = ( REF NODE tree )STRING: IF tree IS nil node THEN # no node # "" ELSE # hae at least one node # STRING result := ""; INT child count = CHILDCOUNT tree; result +:= table + nl + tr + nl + td + " colspan=""" + whole( IF child count < 1 THEN 1 ELSE child count FI, 0 ) + """>" + nbsp + value OF tree + nbsp + dt + nl + rt + nl ; IF child count > 0 THEN # the node has branches # REF NODE child := child OF tree; INT child number := 1; INT mid child = ( child count + 1 ) OVER 2; child := child OF tree; result +:= tr + nl; WHILE child ISNT nil node DO result +:= td + ">" + nl + IF CHILDCOUNT child < 1 THEN nbsp + value OF child + nbsp ELSE TOHTML child FI + dt + nl; child := sibling OF child OD; result +:= rt + nl FI; result +:= elbat + nl FI # TOHTML # ;

test the tree visualisation #

returns a new node with the specified value and no child or siblings #

PROC new node = ( STRING value )REF NODE: HEAP NODE := NODE( value, nil node, nil node );

appends a sibling node to the node n, returns the sibling #

OP +:= = ( REF NODE n, REF NODE sibling node )REF NODE: BEGIN REF NODE sibling := n; WHILE REF NODE( sibling OF sibling ) ISNT nil node DO sibling := sibling OF sibling OD; sibling OF sibling := sibling node END # +:= # ;

appends a new sibling node to the node n, returns the sibling #

OP +:= = ( REF NODE n, STRING sibling value )REF NODE: n +:= new node( sibling value );

adds a child node to the node n, returns the child #

OP /:= = ( REF NODE n, REF NODE child node )REF NODE: child OF n := child node;

adda a new child node to the node n, returns the child #

OP /:= = ( REF NODE n, STRING child value )REF NODE: n /:= new node( child value ); NODE animals := new node( "animals" ); NODE fish := new node( "fish" ); NODE reptiles := new node( "reptiles" ); NODE mammals := new node( "mammals" ); NODE primates := new node( "primates" ); NODE sharks := new node( "sharks" ); sharks /:= "great-white" +:= "hammer-head"; fish /:= "cod" +:= sharks +:= "piranha"; reptiles /:= "iguana" +:= "brontosaurus"; primates /:= "gorilla" +:= "lemur"; mammals /:= "sloth" +:= "horse" +:= "bison" +:= primates; animals /:= fish +:= reptiles +:= mammals; print( ( TOHTML animals ) )</lang>

Output:

animals

fish

cod

sharks
great-white	hammer-head

piranha

reptiles
iguana	brontosaurus

mammals

sloth

horse

bison

primates
gorilla	lemur

AppleScript

Using UTF8 box-drawing characters in a monospaced font, with options for (1.) compacted vs vertically centered display, and (2.) retaining or pruning out nodeless lines of text.

Translation of: Python

Translation of: JavaScript

<lang AppleScript>-- Vertically centered textual tree using UTF8 monospaced -- box-drawing characters, with options for compacting -- and pruning.

-- ┌── Gamma -- ┌─ Beta ┼── Delta -- │ └ Epsilon -- Alpha ┼─ Zeta ───── Eta -- │ ┌─── Iota -- └ Theta ┼── Kappa -- └─ Lambda

-- TESTS -------------------------------------------------- on run

   set tree to Node(1, ¬
       {Node(2, ¬
           {Node(4, {Node(7, {})}), ¬
               Node(5, {})}), ¬
           Node(3, ¬
               {Node(6, ¬
                   {Node(8, {}), Node(9, {})})})})
   
   set tree2 to Node("Alpha", ¬
       {Node("Beta", ¬
           {Node("Gamma", {}), ¬
               Node("Delta", {}), ¬
               Node("Epsilon", {})}), ¬
           Node("Zeta", {Node("Eta", {})}), ¬
           Node("Theta", ¬
               {Node("Iota", {}), Node("Kappa", {}), ¬
                   Node("Lambda", {})})})
   
   set strTrees to unlines({"(NB – view in mono-spaced font)\n\n", ¬
       "Compacted (not all parents vertically centered):\n", ¬
       drawTree2(true, false, tree), ¬
       "\nFully expanded and vertically centered:\n", ¬
       drawTree2(false, false, tree2), ¬
       "\nVertically centered, with nodeless lines pruned out:\n", ¬
       drawTree2(false, true, tree2)})
   set the clipboard to strTrees
   strTrees

end run

-- drawTree2 :: Bool -> Bool -> Tree String -> String on drawTree2(blnCompressed, blnPruned, tree)

   -- Tree design and algorithm inspired by the Haskell snippet at:
   -- https://doisinkidney.com/snippets/drawing-trees.html
   script measured
       on |λ|(t)
           script go
               on |λ|(x)
                   set s to " " & x & " "
                   Tuple(length of s, s)
               end |λ|
           end script
           fmapTree(go, t)
       end |λ|
   end script
   set measuredTree to |λ|(tree) of measured
   
   script levelMax
       on |λ|(a, level)
           a & maximum(map(my fst, level))
       end |λ|
   end script
   set levelWidths to foldl(levelMax, {}, ¬
       init(levels(measuredTree)))
   
   -- Lefts, Mid, Rights
   script lmrFromStrings
       on |λ|(xs)
           set {ls, rs} to items 2 thru -2 of ¬
               (splitAt((length of xs) div 2, xs) as list)
           Tuple3(ls, item 1 of rs, rest of rs)
       end |λ|
   end script
   
   script stringsFromLMR
       on |λ|(lmr)
           script add
               on |λ|(a, x)
                   a & x
               end |λ|
           end script
           foldl(add, {}, items 2 thru -2 of (lmr as list))
       end |λ|
   end script
   
   script fghOverLMR
       on |λ|(f, g, h)
           script
               property mg : mReturn(g)
               on |λ|(lmr)
                   set {ls, m, rs} to items 2 thru -2 of (lmr as list)
                   Tuple3(map(f, ls), |λ|(m) of mg, map(h, rs))
               end |λ|
           end script
       end |λ|
   end script
   
   script lmrBuild
       on leftPad(n)
           script
               on |λ|(s)
                   replicateString(n, space) & s
               end |λ|
           end script
       end leftPad
       
       -- lmrBuild main
       on |λ|(w, f)
           script
               property mf : mReturn(f)
               on |λ|(wsTree)
                   set xs to nest of wsTree
                   set lng to length of xs
                   set {nChars, x} to items 2 thru -2 of ¬
                       ((root of wsTree) as list)
                   set _x to replicateString(w - nChars, "─") & x
                   
                   -- LEAF NODE ------------------------------------
                   if 0 = lng then
                       Tuple3({}, _x, {})
                       
                   else if 1 = lng then
                       -- NODE WITH SINGLE CHILD ---------------------
                       set indented to leftPad(1 + w)
                       script lineLinked
                           on |λ|(z)
                               _x & "─" & z
                           end |λ|
                       end script
                       |λ|(|λ|(item 1 of xs) of mf) of ¬
                           (|λ|(indented, lineLinked, indented) of ¬
                               fghOverLMR)
                   else
                       -- NODE WITH CHILDREN -------------------------
                       script treeFix
                           on cFix(x)
                               script
                                   on |λ|(xs)
                                       x & xs
                                   end |λ|
                               end script
                           end cFix
                           
                           on |λ|(l, m, r)
                               compose(stringsFromLMR, ¬
                                   |λ|(cFix(l), cFix(m), cFix(r)) of ¬
                                   fghOverLMR)
                           end |λ|
                       end script
                       
                       script linked
                           on |λ|(s)
                               set c to text 1 of s
                               set t to tail(s)
                               if "┌" = c then
                                   _x & "┬" & t
                               else if "│" = c then
                                   _x & "┤" & t
                               else if "├" = c then
                                   _x & "┼" & t
                               else
                                   _x & "┴" & t
                               end if
                           end |λ|
                       end script
                       
                       set indented to leftPad(w)
                       set lmrs to map(f, xs)
                       if blnCompressed then
                           set sep to {}
                       else
                           set sep to {"│"}
                       end if
                       
                       tell lmrFromStrings
                           set tupleLMR to |λ|(intercalate(sep, ¬

(|λ|(" ", "┌", "│") of treeFix)} & ¬ map(|λ|("│", "├", "│") of treeFix, ¬ init(tail(lmrs))) & ¬

(|λ|("│", "└", " ") of treeFix)})) end tell

(tupleLMR) of ¬

                           (|λ|(indented, linked, indented) of fghOverLMR)
                   end if
               end |λ|
           end script
       end |λ|
   end script
   
   set treeLines to |λ|(|λ|(measuredTree) of ¬
       foldr(lmrBuild, 0, levelWidths)) of stringsFromLMR
   if blnPruned then
       script notEmpty
           on |λ|(s)
               script isData
                   on |λ|(c)
                       "│ " does not contain c
                   end |λ|
               end script
               any(isData, characters of s)
           end |λ|
       end script
       set xs to filter(notEmpty, treeLines)
   else
       set xs to treeLines
   end if
   unlines(xs)

end drawTree2

-- GENERIC ------------------------------------------------

-- Node :: a -> [Tree a] -> Tree a on Node(v, xs)

   {type:"Node", root:v, nest:xs}

end Node

-- Tuple (,) :: a -> b -> (a, b) on Tuple(a, b)

   -- Constructor for a pair of values, possibly of two different types.
   {type:"Tuple", |1|:a, |2|:b, length:2}

end Tuple

-- Tuple3 (,,) :: a -> b -> c -> (a, b, c) on Tuple3(x, y, z)

   {type:"Tuple3", |1|:x, |2|:y, |3|:z, length:3}

end Tuple3

-- Applied to a predicate and a list, -- |any| returns true if at least one element of the -- list satisfies the predicate. -- any :: (a -> Bool) -> [a] -> Bool on any(f, xs)

   tell mReturn(f)
       set lng to length of xs
       repeat with i from 1 to lng
           if |λ|(item i of xs) then return true
       end repeat
       false
   end tell

end any

-- compose (<<<) :: (b -> c) -> (a -> b) -> a -> c on compose(f, g)

   script
       property mf : mReturn(f)
       property mg : mReturn(g)
       on |λ|(x)

(|λ|(x) of mg) of mf

       end |λ|
   end script

end compose

-- concat :: a -> [a] -- concat :: [String] -> String on concat(xs)

   set lng to length of xs
   if 0 < lng and string is class of (item 1 of xs) then
       set acc to ""
   else
       set acc to {}
   end if
   repeat with i from 1 to lng
       set acc to acc & item i of xs
   end repeat
   acc

end concat

-- concatMap :: (a -> [b]) -> [a] -> [b] on concatMap(f, xs)

   set lng to length of xs
   set acc to {}
   tell mReturn(f)
       repeat with i from 1 to lng
           set acc to acc & (|λ|(item i of xs, i, xs))
       end repeat
   end tell
   return acc

end concatMap

-- filter :: (a -> Bool) -> [a] -> [a] on filter(f, xs)

   tell mReturn(f)
       set lst to {}
       set lng to length of xs
       repeat with i from 1 to lng
           set v to item i of xs
           if |λ|(v, i, xs) then set end of lst to v
       end repeat
       return lst
   end tell

end filter

-- fmapTree :: (a -> b) -> Tree a -> Tree b on fmapTree(f, tree)

   script go
       property g : |λ| of mReturn(f)
       on |λ|(x)
           set xs to nest of x
           if xs ≠ {} then
               set ys to map(go, xs)
           else
               set ys to xs
           end if
           Node(g(root of x), ys)
       end |λ|
   end script

(tree) of go

end fmapTree

-- foldl :: (a -> b -> a) -> a -> [b] -> a on foldl(f, startValue, xs)

   tell mReturn(f)
       set v to startValue
       set lng to length of xs
       repeat with i from 1 to lng
           set v to |λ|(v, item i of xs, i, xs)
       end repeat
       return v
   end tell

end foldl

-- foldr :: (a -> b -> b) -> b -> [a] -> b on foldr(f, startValue, xs)

   tell mReturn(f)
       set v to startValue
       set lng to length of xs
       repeat with i from lng to 1 by -1
           set v to |λ|(item i of xs, v, i, xs)
       end repeat
       return v
   end tell

end foldr

-- fst :: (a, b) -> a on fst(tpl)

   if class of tpl is record then

of tpl

   else
       item 1 of tpl
   end if

end fst

-- identity :: a -> a on identity(x)

   -- The argument unchanged.
   x

end identity

-- init :: [a] -> [a] -- init :: [String] -> [String] on init(xs)

   set blnString to class of xs = string
   set lng to length of xs
   
   if lng > 1 then
       if blnString then
           text 1 thru -2 of xs
       else
           items 1 thru -2 of xs
       end if
   else if lng > 0 then
       if blnString then
           ""
       else
           {}
       end if
   else
       missing value
   end if

end init

-- intercalate :: [a] -> a -> [a] -- intercalate :: String -> [String] -> String on intercalate(sep, xs)

   concat(intersperse(sep, xs))

end intercalate

-- intersperse(0, [1,2,3]) -> [1, 0, 2, 0, 3] -- intersperse :: a -> [a] -> [a] -- intersperse :: Char -> String -> String on intersperse(sep, xs)

   set lng to length of xs
   if lng > 1 then
       set acc to {item 1 of xs}
       repeat with i from 2 to lng
           set acc to acc & {sep, item i of xs}
       end repeat
       if class of xs is string then
           concat(acc)
       else
           acc
       end if
   else
       xs
   end if

end intersperse

-- isNull :: [a] -> Bool -- isNull :: String -> Bool on isNull(xs)

   if class of xs is string then
       "" = xs
   else
       {} = xs
   end if

end isNull

-- iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a] on iterateUntil(p, f, x)

   script
       property mp : mReturn(p)'s |λ|
       property mf : mReturn(f)'s |λ|
       property lst : {x}
       on |λ|(v)
           repeat until mp(v)
               set v to mf(v)
               set end of lst to v
           end repeat
           return lst
       end |λ|
   end script

(x) of result

end iterateUntil

-- levels :: Tree a -> a on levels(tree)

   script nextLayer
       on |λ|(xs)
           script
               on |λ|(x)
                   nest of x
               end |λ|
           end script
           concatMap(result, xs)
       end |λ|
   end script
   
   script roots
       on |λ|(xs)
           script
               on |λ|(x)
                   root of x
               end |λ|
           end script
           map(result, xs)
       end |λ|
   end script
   
   map(roots, iterateUntil(my isNull, nextLayer, {tree}))

end levels

-- map :: (a -> b) -> [a] -> [b] on map(f, xs)

   -- The list obtained by applying f
   -- to each element of xs.
   tell mReturn(f)
       set lng to length of xs
       set lst to {}
       repeat with i from 1 to lng
           set end of lst to |λ|(item i of xs, i, xs)
       end repeat
       return lst
   end tell

end map

-- maximum :: Ord a => [a] -> a on maximum(xs)

   script
       on |λ|(a, b)
           if a is missing value or b > a then
               b
           else
               a
           end if
       end |λ|
   end script
   foldl(result, missing value, xs)

end maximum

-- mReturn :: First-class m => (a -> b) -> m (a -> b) on mReturn(f)

   -- 2nd class handler function lifted into 1st class script wrapper. 
   if script is class of f then
       f
   else
       script
           property |λ| : f
       end script
   end if

end mReturn

-- replicateString :: Int -> String -> String on replicateString(n, s)

   set out to ""
   if n < 1 then return out
   set dbl to s
   
   repeat while (n > 1)
       if (n mod 2) > 0 then set out to out & dbl
       set n to (n div 2)
       set dbl to (dbl & dbl)
   end repeat
   return out & dbl

end replicateString

-- snd :: (a, b) -> b on snd(tpl)

   if class of tpl is record then

of tpl

   else
       item 2 of tpl
   end if

end snd

-- splitAt :: Int -> [a] -> ([a], [a]) on splitAt(n, xs)

   if n > 0 and n < length of xs then
       if class of xs is text then
           Tuple(items 1 thru n of xs as text, items (n + 1) thru -1 of xs as text)
       else
           Tuple(items 1 thru n of xs, items (n + 1) thru -1 of xs)
       end if
   else
       if n < 1 then
           Tuple({}, xs)
       else
           Tuple(xs, {})
       end if
   end if

end splitAt

-- tail :: [a] -> [a] on tail(xs)

   set blnText to text is class of xs
   if blnText then
       set unit to ""
   else
       set unit to {}
   end if
   set lng to length of xs
   if 1 > lng then
       missing value
   else if 2 > lng then
       unit
   else
       if blnText then
           text 2 thru -1 of xs
       else
           rest of xs
       end if
   end if

end tail

-- unlines :: [String] -> String on unlines(xs)

   -- A single string formed by the intercalation
   -- of a list of strings with the newline character.
   set {dlm, my text item delimiters} to ¬
       {my text item delimiters, linefeed}
   set str to xs as text
   set my text item delimiters to dlm
   str

end unlines</lang>

Output:

(NB – view in mono-spaced font)


Compacted (not all parents vertically centered):

       ┌ 4 ─ 7 
   ┌ 2 ┴ 5 
 1 ┤       ┌ 8 
   └ 3 ─ 6 ┴ 9 

Fully expanded and vertically centered:

               ┌── Gamma 
               │
       ┌─ Beta ┼── Delta 
       │       │
       │       └ Epsilon 
       │
 Alpha ┼─ Zeta ───── Eta 
       │
       │       ┌─── Iota 
       │       │
       └ Theta ┼── Kappa 
               │
               └─ Lambda 

Vertically centered, with nodeless lines pruned out:

               ┌── Gamma 
       ┌─ Beta ┼── Delta 
       │       └ Epsilon 
 Alpha ┼─ Zeta ───── Eta 
       │       ┌─── Iota 
       └ Theta ┼── Kappa 
               └─ Lambda

Batch File

Displays a tree of the current directory. <lang batch file>@tree %cd%</lang>

BBC BASIC

Works with: BBC BASIC for Windows

This creates a native Windows Tree View control: <lang bbcbasic> INSTALL @lib$+"WINLIB5"

     ON ERROR SYS "MessageBox", @hwnd%, REPORT$, 0, 0 : QUIT
     
     REM!WC Windows constants:
     TVI_SORT = -65533
     TVIF_TEXT = 1
     TVM_INSERTITEM = 4352
     TVS_HASBUTTONS = 1
     TVS_HASLINES = 2
     TVS_LINESATROOT = 4
     
     REM. TV_INSERTSTRUCT
     DIM tvi{hParent%,       \
     \       hInsertAfter%,  \
     \       mask%,          \
     \       hItem%,         \
     \       state%,         \
     \       stateMask%,     \
     \       pszText%,       \
     \       cchTextMax%,    \
     \       iImage%,        \
     \       iSelectedImage%,\
     \       cChildren%,     \
     \       lParam%         \
     \      }
     
     SYS "InitCommonControls"
     hTree% = FN_createwindow("SysTreeView32", "", 0, 0, @vdu.tr%, @vdu.tb%, 0, \
     \                        TVS_HASLINES OR TVS_HASBUTTONS OR TVS_LINESATROOT, 0)
     hroot% = FNinsertnode(0, "Root")
     hchild1% = FNinsertnode(hroot%, "Child 1")
     hchild2% = FNinsertnode(hroot%, "Child 2")
     hchild11% = FNinsertnode(hchild1%, "Grandchild 1")
     hchild12% = FNinsertnode(hchild1%, "Grandchild 2")
     hchild21% = FNinsertnode(hchild2%, "Grandchild 3")
     hchild22% = FNinsertnode(hchild2%, "Grandchild 4")
     
     REPEAT
       WAIT 1
     UNTIL FALSE
     END
     
     DEF FNinsertnode(hparent%, text$)
     LOCAL hnode%
     text$ += CHR$0
     
     tvi.hParent% = hparent%
     tvi.hInsertAfter% = TVI_SORT
     tvi.mask% = TVIF_TEXT
     tvi.pszText% = !^text$
     
     SYS "SendMessage", hTree%, TVM_INSERTITEM, 0, tvi{} TO hnode%
     IF hnode% = 0 ERROR 100, "TVM_INSERTITEM failed"
     SYS "InvalidateRect", hTree%, 0, 0
     = hnode%</lang>

C

Print a simple tree to standard output: <lang c>#include <stdio.h>

include <stdlib.h>

typedef struct stem_t *stem; struct stem_t { const char *str; stem next; };

void tree(int root, stem head) { static const char *sdown = " |", *slast = " `", *snone = " "; struct stem_t col = {0, 0}, *tail;

for (tail = head; tail; tail = tail->next) { printf("%s", tail->str); if (!tail->next) break; }

printf("--%d\n", root);

if (root <= 1) return;

if (tail && tail->str == slast) tail->str = snone;

if (!tail) tail = head = &col; else tail->next = &col;

while (root) { // make a tree by doing something random int r = 1 + (rand() % root); root -= r; col.str = root ? sdown : slast;

tree(r, head); }

tail->next = 0; }

int main(int c, char**v) { int n; if (c < 2 || (n = atoi(v[1])) < 0) n = 8;

tree(n, 0); return 0; }</lang>

Output:

--8
  `--8
     |--7
     |  |--3
     |  |  |--2
     |  |  |  `--2
     |  |  |     `--2
     |  |  |        |--1
     |  |  |        `--1
     |  |  `--1
     |  |--2
     |  |  |--1
     |  |  `--1
     |  |--1
     |  `--1
     `--1

C++

<lang cpp>#include <functional>

include <iostream>
include <random>

class BinarySearchTree { private:

   struct Node {
       int key;
       Node *left, *right;

       Node(int k) : key(k), left(nullptr), right(nullptr) {
           //empty
       }
   } *root;

public:

   BinarySearchTree() : root(nullptr) {
       // empty
   }

   bool insert(int key) {
       if (root == nullptr) {
           root = new Node(key);
       } else {
           auto n = root;
           Node *parent;
           while (true) {
               if (n->key == key) {
                   return false;
               }

               parent = n;

               bool goLeft = key < n->key;
               n = goLeft ? n->left : n->right;

               if (n == nullptr) {
                   if (goLeft) {
                       parent->left = new Node(key);
                   } else {
                       parent->right = new Node(key);
                   }
                   break;
               }
           }
       }
       return true;
   }

   friend std::ostream &operator<<(std::ostream &, const BinarySearchTree &);

};

template<typename T> void display(std::ostream &os, const T *n) {

   if (n != nullptr) {
       os << "Node(";

       display(os, n->left);

       os << ',' << n->key << ',';

       display(os, n->right);

       os << ")";
   } else {
       os << '-';
   }

}

std::ostream &operator<<(std::ostream &os, const BinarySearchTree &bst) {

   display(os, bst.root);
   return os;

}

int main() {

   std::default_random_engine generator;
   std::uniform_int_distribution<int> distribution(0, 200);
   auto rng = std::bind(distribution, generator);

   BinarySearchTree tree;

   tree.insert(100);
   for (size_t i = 0; i < 20; i++) {
       tree.insert(rng());
   }
   std::cout << tree << '\n';

   return 0;

}</lang>

Output:

Node(Node(Node(Node(Node(-,4,-),17,Node(-,22,-)),28,-),30,Node(Node(-,36,-),48,Node(Node(Node(-,77,-),81,-),91,-))),100,Node(Node(Node(Node(-,117,-),125,Node(Node(-,131,-),151,Node(-,158,Node(-,163,-)))),176,Node(Node(-,192,-),193,-)),200,-))

C#

<lang csharp>using System;

public static class VisualizeTree {

   public static void Main() {
       "A".t(
           "B0".t(
               "C1",
               "C2".t(
                   "D".t("E1", "E2", "E3")),
               "C3".t(
                   "F1",
                   "F2",
                   "F3".t("G"),
                   "F4".t("H1", "H2"))),
           "B1".t(
               "K1",
               "K2".t(
                   "L1".t("M"),
                   "L2",
                   "L3"),
               "K3")
       ).Print();
   }

   private static Tree t(this string value, params Tree[] children) => new Tree(value, children);

   private static void Print(this Tree tree) => tree.Print(true, "");

   private static void Print(this Tree tree, bool last, string prefix) {
       (string current, string next) = last
           ? (prefix + "└─" + tree.Value, prefix + "  ")
           : (prefix + "├─" + tree.Value, prefix + "| ");
       Console.WriteLine(current[2..]);
       for (int c = 0; c < tree.Children.Length; c++) {
           tree.Children[c].Print(c == tree.Children.Length - 1, next);
       }
   }

   class Tree
   {
       public Tree(string value, params Tree[] children) => (Value, Children) = (value, children);
       public static implicit operator Tree(string value) => new Tree(value);
       public string Value { get; }
       public Tree[] Children { get; }
   }

}</lang>

Output:

A
├─B0
| ├─C1
| ├─C2
| | └─D
| |   ├─E1
| |   ├─E2
| |   └─E3
| └─C3
|   ├─F1
|   ├─F2
|   ├─F3
|   | └─G
|   └─F4
|     ├─H1
|     └─H2
└─B1
  ├─K1
  ├─K2
  | ├─L1
  | | └─M
  | ├─L2
  | └─L3
  └─K3

Clojure

<lang clojure>(use 'vijual)

(draw-tree [[:A] [:B] [:C [:D [:E] [:F]] [:G]]]) </lang>

Output:

+---+ +---+ +---+
| A | | B | | C |
+---+ +---+ +-+-+
              |
        +-----+
        |     |
      +-+-+ +-+-+
      | D | | G |
      +-+-+ +---+
        |
     +--+--+
     |     |
   +-+-+ +-+-+
   | E | | F |
   +---+ +---+

Common Lisp

<lang lisp>(defun visualize (tree)

 (labels
     ((rprint (list)
        (mapc #'princ (reverse list)))
      (vis-h (tree branches)
        (let ((len (length tree)))
          (loop
             for item in tree
             for idx from 1 to len do
               (cond
                 ((listp item)
                  (rprint (cdr branches))
                  (princ "+---+")
                  (let ((next (cons "|   "
                                    (if (= idx len)
                                        (cons "    " (cdr branches))
                                        branches))))
                    (terpri)
                    (rprint (if (null item)
                                (cdr next)
                                next))
                    (terpri)
                    (vis-h item next)))
                 (t
                  (rprint (cdr branches))
                  (princ item)
                  (terpri)
                  (rprint (if (= idx len)
                              (cdr branches)
                              branches))
                  (terpri)))))))
   (vis-h tree '("|   "))))</lang>

Output:

<lang lisp>CL-USER> (visualize '(a b c ((d (e ((() ()))) f)) (g))) A

B

C

+---+

D

+---+

|

E

|

+---+

|

+---+

|

+---+

|

+---+

F

+---+

NIL</lang> or <lang lisp>(use-package :iterate) (defun print-tree (tree value-function children-function)

 (labels
     ((do-print-tree (tree prefix)
        (format t "~a~%" (funcall value-function tree))
        (iter
          (with children = (funcall children-function tree))
          (for child = (pop children))
          (while child)
       
          (if children
              (progn (format t "~a├─ " prefix)
                     (do-print-tree child (format nil "~a│  " prefix)))
              (progn (format t "~a└─ " prefix)
                     (do-print-tree child (format nil "~a   " prefix)))))))
   (do-print-tree tree "")))

</lang>

Output:

<lang lisp>CL-USER>(print-tree '(a

             (aa
              (aaa
               (aaaa)
               (aaab
                (aaaba)
                (aaabb))
               (aaac)))
             (ab)
             (ac
              (aca)
              (acb)
              (acc)))
           #'car #'cdr)

A ├─ AA │ └─ AAA │ ├─ AAAA │ ├─ AAAB │ │ ├─ AAABA │ │ └─ AAABB │ └─ AAAC ├─ AB └─ AC

  ├─ ACA
  ├─ ACB
  └─ ACC

</lang>

D

Translation of: Haskell

<lang d>import std.stdio, std.conv, std.algorithm, std.array;

struct Node(T) { T value; Node* left, right; }

string[] treeIndent(T)(in Node!T* t) pure nothrow @safe {

   if (!t) return ["-- (null)"];
   const tr = t.right.treeIndent;
   return "--" ~ t.value.text ~
          t.left.treeIndent.map!q{"  |" ~ a}.array ~
          ("  `" ~ tr[0]) ~ tr[1 .. $].map!q{"   " ~ a}.array;

}

void main () {

   static N(T)(T v, Node!T* l=null, Node!T* r=null) {
       return new Node!T(v, l, r);
   }

   const tree = N(1, N(2, N(4, N(7)), N(5)), N(3, N(6, N(8), N(9))));
   writefln("%-(%s\n%)", tree.treeIndent);

}</lang>

Output:

--1
  |--2
  |  |--4
  |  |  |--7
  |  |  |  |-- (null)
  |  |  |  `-- (null)
  |  |  `-- (null)
  |  `--5
  |     |-- (null)
  |     `-- (null)
  `--3
     |--6
     |  |--8
     |  |  |-- (null)
     |  |  `-- (null)
     |  `--9
     |     |-- (null)
     |     `-- (null)
     `-- (null)

Delphi

Library: System.SysUtils

Translation of: Go

<lang Delphi> program Visualize_a_tree;

{$APPTYPE CONSOLE}

uses

 System.SysUtils;

type

 TNode = record
   _label: string;
   children: TArray<Integer>;
 end;

 TTree = TArray<TNode>;

 TTreeHelper = record helper for TTree
   procedure AddNode(lb: string; chl: TArray<Integer> = []);
 end;

procedure Vis(t: TTree);

 procedure f(n: Integer; pre: string);
 begin
   var ch := t[n].children;
   if Length(ch) = 0 then
   begin
     Writeln('-', t[n]._label);
     exit;
   end;

   writeln('+', t[n]._label);
   var last := Length(ch) - 1;
   for var c in copy(ch, 0, last) do
   begin
     write(pre, '+-');
     f(c, pre + '¦ ');
   end;
   write(pre, '+-');
   f(ch[last], pre + '  ');
 end;

begin

 if Length(t) = 0 then
 begin
   writeln('<empty>');
   exit;
 end;

 f(0, );

end;

{ TTreeHelper }

procedure TTreeHelper.AddNode(lb: string; chl: TArray<Integer> = []); begin

 SetLength(self, Length(self) + 1);
 with self[High(self)] do
 begin
   _label := lb;
   if Length(chl) > 0 then
     children := copy(chl, 0, length(chl));
 end;

end;

var

 Tree: TTree;

begin

 Tree.AddNode('root', [1, 2, 3]);
 Tree.AddNode('ei', [4, 5]);
 Tree.AddNode('bee');
 Tree.AddNode('si');
 Tree.AddNode('dee');
 Tree.AddNode('y', [6]);
 Tree.AddNode('eff');

 Vis(Tree);

 {$IFNDEF UNIX} readln; {$ENDIF}

end.</lang>

Output:

┐root
├─┐ei
│ ├──dee
│ └─┐y
│   └──eff
├──bee
└──si

Elena

ELENA 5.0 : <lang elena>import system'routines; import extensions;

class Node {

   string theValue;
   Node[] theChildren;
   
   constructor new(string value, Node[] children)
   {
       theValue := value;
               
       theChildren := children;
   }
   
   constructor new(string value)
       <= new(value, new Node[](0));
       
   constructor new(Node[] children)
       <= new(emptyString, children);
       
   get() = theValue;
   
   Children = theChildren;

}

extension treeOp {

   writeTree(node, prefix)
   {
       var children := node.Children;
       var length := children.Length;
       
       children.zipForEach(new Range(1, length), (child,index)
       {
           self.printLine(prefix,"|");
           self.printLine(prefix,"+---",child.get());                
           
           var nodeLine := prefix + (index==length).iif("    ","|   ");
           
           self.writeTree(child,nodeLine);
       });
       
       ^ self
   }
   
   writeTree(node)
       = self.writeTree(node,"");

}

public program() {

   var tree := Node.new(
                new Node[]{
                   Node.new("a", new Node[]
                   {
                       Node.new("b", new Node[]{Node.new("c")}),
                       Node.new("d")
                   }),
                   Node.new("e")
                });
                
   console.writeTree(tree).readChar()

}</lang>

Output:

|
+---a
|   |
|   +---b
|   |   |
|   |   +---c
|   |
|   +---d
|
+---e

Erlang

Until real code shows up, I follow the lead of Python and print tuples with a width of 1.

Output:

9> io:fwrite("~1p", [{1, 2, {30, 40}, {{500, 600}, 70}}]).
{1,
 2,
 {30,
  40},
 {{500,
   600},
  70}}

F#

<lang fsharp>type tree =

T of string * tree list

let prefMid = seq { yield "├─"; while true do yield "│ " } let prefEnd = seq { yield "└─"; while true do yield " " } let prefNone = seq { while true do yield "" }

let c2 x y = Seq.map2 (fun u v -> String.concat "" [u; v]) x y

let rec visualize (T(label, children)) pre =

   seq {
       yield (Seq.head pre) + label
       if children <> [] then
           let preRest = Seq.skip 1 pre
           let last = Seq.last (List.toSeq children)
           for e in children do
               if e = last then yield! visualize e (c2 preRest prefEnd)
               else yield! visualize e (c2 preRest prefMid)
   }

let example =

   T ("root",
           [T ("a", 
                   [T ("a1",
                           [T ("a11", []);
                           T ("a12", []) ]) ]);
           T ("b",
                   [T ("b1", []) ]) ])

visualize example prefNone

> Seq.iter (printfn "%s")</lang>

Output:

root
├─a
│ └─a1
│   ├─a11
│   └─a12
└─b
  └─b1

Factor

Factor's prettyprinter does this by default with any nested sequences and/or tuples. There are dynamic variables that can be altered to change the prettyprinter's default behavior. The most interesting are tab-size and margin for customizing the look of a tree. For smaller trees, it's best to change margin from its default of 64 to something low, perhaps 10. <lang factor>USE: literals

CONSTANT: mammals { "mammals" { "deer" "gorilla" "dolphin" } } CONSTANT: reptiles { "reptiles" { "turtle" "lizard" "snake" } }

{ "animals" ${ mammals reptiles } } dup . 10 margin set .</lang>

Output:

{
    "animals"
    {
        { "mammals" { "deer" "gorilla" "dolphin" } }
        { "reptiles" { "turtle" "lizard" "snake" } }
    }
}
{
    "animals"
    {
        {
            "mammals"
            {
                "deer"
                "gorilla"
                "dolphin"
            }
        }
        {
            "reptiles"
            {
                "turtle"
                "lizard"
                "snake"
            }
        }
    }
}

An example showcasing tuples by displaying an AVL tree: <lang factor>USE: trees.avl AVL{ { 1 2 } { 9 19 } { 3 4 } { 5 6 } } .</lang>

Output:

T{ avl
    { root
        T{ avl-node
            { key 3 }
            { value 4 }
            { left
                T{ avl-node
                    { key 1 }
                    { value 2 }
                    { balance 0 }
                }
            }
            { right
                T{ avl-node
                    { key 9 }
                    { value 19 }
                    { left
                        T{ avl-node
                            { key 5 }
                            { value 6 }
                            { balance 0 }
                        }
                    }
                    { balance -1 }
                }
            }
            { balance 1 }
        }
    }
    { count 4 }
}

Fōrmulæ

Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text. Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for storage and transfer purposes more than visualization and edition.

Programs in Fōrmulæ are created/edited online in its website, However they run on execution servers. By default remote servers are used, but they are limited in memory and processing power, since they are intended for demonstration and casual use. A local server can be downloaded and installed, it has no limitations (it runs in your own computer). Because of that, example programs can be fully visualized and edited, but some of them will not run if they require a moderate or heavy computation/memory resources, and no local server is being used.

In this page you can see the program(s) related to this task and their results.

Go

JSON

Not the most economical output, but at least json.MarshalIndent is in the Go standard library. Note that the definition of Node has nothing JSON specific about it; it's an ordinary struct. <lang Go>package main

import (

   "encoding/json"
   "fmt"
   "log"

)

type Node struct {

   Name     string
   Children []*Node

}

func main() {

   tree := &Node{"root", []*Node{
       &Node{"a", []*Node{
           &Node{"d", nil},
           &Node{"e", []*Node{
               &Node{"f", nil},
           }}}},
       &Node{"b", nil},
       &Node{"c", nil},
   }}
   b, err := json.MarshalIndent(tree, "", "   ")
   if err != nil {
       log.Fatal(err)
   }
   fmt.Println(string(b))

}</lang>

Output:

{
   "Name": "root",
   "Children": [
      {
         "Name": "a",
         "Children": [
            {
               "Name": "d",
               "Children": null
            },
            {
               "Name": "e",
               "Children": [
                  {
                     "Name": "f",
                     "Children": null
                  }
               ]
            }
         ]
      },
      {
         "Name": "b",
         "Children": null
      },
      {
         "Name": "c",
         "Children": null
      }
   ]
}

TOML

It works in this case, but TOML wasn't really designed for this and encoders may have trouble with general trees. Empty trees and nils for example might be problematic depending on your data structures and limitations of your TOML encoder. YMMV. <lang go>package main

import (

   "log"
   "os"

   "github.com/BurntSushi/toml"

)

type Node struct {

   Name     string
   Children []*Node

}

func main() {

   tree := &Node{"root", []*Node{
       &Node{"a", []*Node{
           &Node{"d", nil},
           &Node{"e", []*Node{
               &Node{"f", nil},
           }}}},
       &Node{"b", nil},
       &Node{"c", nil},
   }}
   enc := toml.NewEncoder(os.Stdout)
   enc.Indent = "   "
   err := enc.Encode(tree)
   if err != nil {
       log.Fatal(err)
   }

}</lang>

Output:

Name = "root"

[[Children]]
   Name = "a"

   [[Children.Children]]
      Name = "d"


   [[Children.Children]]
      Name = "e"

      [[Children.Children.Children]]
         Name = "f"


[[Children]]
   Name = "b"


[[Children]]
   Name = "c"

Unicode

A non-library solution, more like a number of other solutions on this page, and with more compact output. The tree representation here uses integer indexes rather than pointers, which is efficient for representation and computation. A serialization format like JSON or TOML wouldn't see it as a hierarchical structure, but the code here knows to interpret the child ints as node indexes. <lang go>package main

import "fmt"

type tree []node

type node struct {

   label    string
   children []int // indexes into tree

}

func main() {

   vis(tree{
       0: node{"root", []int{1, 2, 3}},
       1: node{"ei", []int{4, 5}},
       2: node{"bee", nil},
       3: node{"si", nil},
       4: node{"dee", nil},
       5: node{"y", []int{6}},
       6: node{"eff", nil},
   })

}

func vis(t tree) {

   if len(t) == 0 {
       fmt.Println("<empty>")
       return
   }
   var f func(int, string)
   f = func(n int, pre string) {
       ch := t[n].children
       if len(ch) == 0 {
           fmt.Println("╴", t[n].label)
           return
       }
       fmt.Println("┐", t[n].label)
       last := len(ch) - 1
       for _, ch := range ch[:last] {
           fmt.Print(pre, "├─")
           f(ch, pre+"│ ")
       }
       fmt.Print(pre, "└─")
       f(ch[last], pre+"  ")
   }
   f(0, "")

}</lang>

Output:

┐ root
├─┐ ei
│ ├─╴ dee
│ └─┐ y
│   └─╴ eff
├─╴ bee
└─╴ si

Haskell

Tree borrowed from Tree traversal: <lang haskell>data Tree a = Empty | Node { value :: a, left :: Tree a, right :: Tree a } deriving (Show, Eq)

tree = Node 1 (Node 2 (Node 4 (Node 7 Empty Empty) Empty) (Node 5 Empty Empty)) (Node 3 (Node 6 (Node 8 Empty Empty) (Node 9 Empty Empty)) Empty)

treeIndent Empty = ["-- (nil)"] treeIndent t = ["--" ++ show (value t)] ++ map (" |"++) ls ++ (" `" ++ r):map (" "++) rs where (r:rs) = treeIndent$right t ls = treeIndent$left t

main = mapM_ putStrLn $ treeIndent tree</lang>

Output:

--1
  |--2
  |  |--4
  |  |  |--7
  |  |  |  |-- (nil)
  |  |  |  `-- (nil)
  |  |  `-- (nil)
  |  `--5
  |     |-- (nil)
  |     `-- (nil)
  `--3
     |--6
     |  |--8
     |  |  |-- (nil)
     |  |  `-- (nil)
     |  `--9
     |     |-- (nil)
     |     `-- (nil)
     `-- (nil)

The Data.Tree module in the standard (GHC) libraries also includes a drawTree function for multiway (rose) trees of strings. We can fmap show over our tree of integers to derive a tree of strings, and apply `drawTree` to that.

<lang haskell>import Data.Tree (Tree(..), drawTree)

tree :: Tree Int tree =

 Node
   1
   [ Node 2 [Node 4 [Node 7 []], Node 5 []]
   , Node 3 [Node 6 [Node 8 [], Node 9 []]]
   ]

main :: IO () main = (putStrLn . drawTree . fmap show) tree</lang>

Output:

1
|
+- 2
|  |
|  +- 4
|  |  |
|  |  `- 7
|  |
|  `- 5
|
`- 3
   |
   `- 6
      |
      +- 8
      |
      `- 9

Icon and Unicon

The following works in both languages. <lang unicon>procedure main(A)

   showTree("", " -", [1, [2,[3],[4,[5],[6]],[7,[11]]], [8,[9,[10]]] ])
   write()
   showTree("", " -", [1, [2,[3,[4]]], [5,[6],[7,[8],[9]],[10]] ])

end

procedure showTree(prefix, lastc, A)

   write(prefix, lastc, "--", A[1])
   if *A > 1 then {
       prefix ||:= if prefix[-1] == "|" then "   " else "    "
       every showTree(prefix||"|", "-", !A[2:2 < *A])
       showTree(prefix, "`-", A[*A])
       }

end</lang>

Output:

->tree
 ---1
    |---2
    |   |---3
    |   |---4
    |   |   |---5
    |   |   `---6
    |   `---7
    |       `---11
    `---8
        `---9
            `---10

 ---1
    |---2
    |   `---3
    |       `---4
    `---5
        |---6
        |---7
        |   |---8
        |   `---9
        `---10
->

J

See: j:Essays/Tree Display for tree represented as label pairs.

Or, adapted to the parent index representation of a tree (which allows different nodes to share labels and may also be more convenient for other reasons):

<lang J>BOXC=: 9!:6 NB. box drawing characters EW =: {: BOXC NB. east-west

showtree=: 4 : 0

NB. y is parent index for each node (non-indices for root nodes)
NB. x is label for each node 
t=. (<EW,' ') ,@<@,:@,&":&.> x        NB. tree fragments
c=. |:(#~ e./@|:);(~.,"0&.>(</. i.@#)) y
while. +./ b=. ({.c)*.//.-.e.~/c do.
 i=. b#~.{.c                          NB. parents whose children are leaves
 j=. </./(({.c)e.i)#"1 c              NB. leaves grouped by parents
 t=. a: (;j)}t i}~ (i{t) subtree&.> j{&.><t
 c=. (-.({.c)e.i)#"1 c                NB. prune edges to leaves
end.
;([: ,.&.>/ extend&.>)&> t -. a:

)

subtree=: 4 : 0

p=. EW={."1 s=. >{.t=. graft y
(<(>{.x) root p),(<(connect p),.s),}.t

)

graft=: 3 : 0

n=. (-~ >./) #&> y
f=. i.@(,&0)@#&.>@{.&.> y
,&.>/ y ,&> n$&.>f

)

connect=: 3 : 0

b=. (+./\ *. +./\.) y
c=. (b+2*y){' ',9 3 3{BOXC  NB. │ NS ├ E
c=. (0{BOXC) (b i. 1)}c     NB. ┌ NW
c=. (6{BOXC) (b i: 1)}c     NB. └ SW
j=. (b i. 1)+<.-:+/b
EW&(j})^:(1=+/b) c j}~ ((0 3 6 9{BOXC)i.j{c){1 4 7 5{BOXC

)

root=: 4 : 0

j=. k+<.-:1+(y i: 1)-k=. y i. 1
(-j)|.(#y){.x,.,:' ',EW

)

extend=: 3 : '(+./\"1 (y=EW) *. *./\."1 y e. ,EW)}y,:EW' </lang>

Example use:

<lang j> (i.10) showtree _,}.p:inv i.10

                ┌─ 6
    ┌─ 1 ─── 3 ─┴─ 7
    │           ┌─ 8

─ 0 ─┤ ┌─ 4 ─┴─ 9

    └─ 2 ─┴─ 5    </lang>

For comparison purposes, here's the node labels along with (in the following row) the index of their parent node:

Also, note that labels can be arbitrary. Here, we used numeric labels because they were concise and convenient. But, for example, we can replace the label '0' with 'george' and the label '4' with 'fred':

<lang j> ((<'george') 0} (<'fred') 4} ":each i.10)showtree _,}.p:inv i.10

                        ┌─ 6
         ┌─ 1 ─── 3 ────┴─ 7
         │              ┌─ 8

─ george ─┤ ┌─ fred ─┴─ 9

         └─ 2 ─┴─ 5        </lang>

Java

Minimalist BST that can do nothing except print itself to stdout. <lang java>public class VisualizeTree {

   public static void main(String[] args) {
       BinarySearchTree tree = new BinarySearchTree();

       tree.insert(100);
       for (int i = 0; i < 20; i++)
           tree.insert((int) (Math.random() * 200));
       tree.display();
   }

}

class BinarySearchTree {

   private Node root;

   private class Node {
       private int key;
       private Node left, right;

       Node(int k) {
           key = k;
       }
   }

   public boolean insert(int key) {
       if (root == null)
           root = new Node(key);
       else {
           Node n = root;
           Node parent;
           while (true) {
               if (n.key == key)
                   return false;

               parent = n;

               boolean goLeft = key < n.key;
               n = goLeft ? n.left : n.right;

               if (n == null) {
                   if (goLeft) {
                       parent.left = new Node(key);
                   } else {
                       parent.right = new Node(key);
                   }
                   break;
               }
           }
       }
       return true;
   }

   public void display() {
       final int height = 5, width = 64;

       int len = width * height * 2 + 2;
       StringBuilder sb = new StringBuilder(len);
       for (int i = 1; i <= len; i++)
           sb.append(i < len - 2 && i % width == 0 ? "\n" : ' ');

       displayR(sb, width / 2, 1, width / 4, width, root, " ");
       System.out.println(sb);
   }

   private void displayR(StringBuilder sb, int c, int r, int d, int w, Node n,
           String edge) {
       if (n != null) {
           displayR(sb, c - d, r + 2, d / 2, w, n.left, " /");

           String s = String.valueOf(n.key);
           int idx1 = r * w + c - (s.length() + 1) / 2;
           int idx2 = idx1 + s.length();
           int idx3 = idx1 - w;
           if (idx2 < sb.length())
               sb.replace(idx1, idx2, s).replace(idx3, idx3 + 2, edge);

           displayR(sb, c + d, r + 2, d / 2, w, n.right, "\\ ");
       }
   }

}</lang>

                             100                              
                /                              \               
               49                              106             
        /              \                /              \       
       44              94              105             152     
    /      \        /                               /      \   
   26      47      61                              109     178 
  /  \            /  \                               \    /    
 12  33          51  88                              119 159

JavaScript

HTML

Javascript wrapped in HTML5 document. Should work in modern browsers. <lang html><!doctype html> <html id="doc">

 <head><meta charset="utf-8"/>
   <title>Stuff</title>
   <script type="application/javascript">

function gid(id) { return document.getElementById(id); }

function ce(tag, cls, parent_node) { var e = document.createElement(tag); e.className = cls; if (parent_node) parent_node.appendChild(e); return e; }

function dom_tree(id) { gid('tree').textContent = ""; gid('tree').appendChild(mktree(gid(id), null)); }

function mktree(e, p) { var t = ce("div", "tree", p); var tog = ce("span", "toggle", t); var h = ce("span", "tag", t);

if (e.tagName === undefined) { h.textContent = "#Text"; var txt = e.textContent; if (txt.length > 0 && txt.match(/\S/)) { h = ce("div", "txt", t); h.textContent = txt; } return t; }

tog.textContent = "−"; tog.onclick = function () { clicked(tog); } h.textContent = e.nodeName;

var l = e.childNodes; for (var i = 0; i != l.length; i++) mktree(l[i], t); return t; }

function clicked(e) { var is_on = e.textContent == "−"; e.textContent = is_on ? "+" : "−"; e.parentNode.className = is_on ? "tree-hide" : "tree"; }

   </script>
   <style>
     #tree { white-space: pre; font-family: monospace; border: 1px solid }
     .tree > .tree-hide, .tree > .tree

{ margin-left: 2em; border-left: 1px dotted rgba(0,0,0,.2)}

     .tree-hide > .tree, .tree-hide > .tree-hide { display: none }
     .tag { color: navy }
     .tree-hide > .tag { color: maroon }
     .txt { color: gray; padding: 0 .5em; margin: 0 .5em 0 2em; border: 1px dotted rgba(0,0,0,.1) }
     .toggle { display: inline-block; width: 2em; text-align: center }
   </style>
 </head>
 <body>
   <article>

Headline

       Blah blah

More headline

Something something

Nested section

Somethin somethin list:

Apples
Oranges
Cetera Fruits

     </section>
   </article>

<a href="javascript:dom_tree('doc')">click me</a>

 </body>

</html></lang>

Plain text

Vertically centered tree

Translation of: Python

(Functional version)

<lang JavaScript>(() => {

   'use strict';

   // UTF8 character-drawn tree, with options for compacting vs
   // centering parents, and for pruning out nodeless lines.

   const example = `
              ┌ Epsilon
      ┌─ Beta ┼─── Zeta
      │       └──── Eta
Alpha ┼ Gamma ─── Theta
      │       ┌─── Iota
      └ Delta ┼── Kappa
              └─ Lambda`

   // drawTree2 :: Bool -> Bool -> Tree String -> String
   const drawTree2 = blnCompact => blnPruned => tree => {
       // Tree design and algorithm inspired by the Haskell snippet at:
       // https://doisinkidney.com/snippets/drawing-trees.html
       const
           // Lefts, Middle, Rights
           lmrFromStrings = xs => {
               const [ls, rs] = Array.from(splitAt(
                   Math.floor(xs.length / 2),
                   xs
               ));
               return Tuple3(ls, rs[0], rs.slice(1));
           },
           stringsFromLMR = lmr =>
           Array.from(lmr).reduce((a, x) => a.concat(x), []),
           fghOverLMR = (f, g, h) => lmr => {
               const [ls, m, rs] = Array.from(lmr);
               return Tuple3(ls.map(f), g(m), rs.map(h));
           };

       const lmrBuild = (f, w) => wsTree => {
           const
               leftPad = n => s => ' '.repeat(n) + s,
               xs = wsTree.nest,
               lng = xs.length,
               [nChars, x] = Array.from(wsTree.root);

           // LEAF NODE --------------------------------------
           return 0 === lng ? (
               Tuple3([], '─'.repeat(w - nChars) + x, [])

               // NODE WITH SINGLE CHILD -------------------------
           ) : 1 === lng ? (() => {
               const indented = leftPad(1 + w);
               return fghOverLMR(
                   indented,
                   z => '─'.repeat(w - nChars) + x + '─' + z,
                   indented
               )(f(xs[0]));

               // NODE WITH CHILDREN -----------------------------
           })() : (() => {
               const
                   cFix = x => xs => x + xs,
                   treeFix = (l, m, r) => compose(
                       stringsFromLMR,
                       fghOverLMR(cFix(l), cFix(m), cFix(r))
                   ),
                   _x = '─'.repeat(w - nChars) + x,
                   indented = leftPad(w),
                   lmrs = xs.map(f);
               return fghOverLMR(
                   indented,
                   s => _x + ({
                       '┌': '┬',
                       '├': '┼',
                       '│': '┤',
                       '└': '┴'
                   })[s[0]] + s.slice(1),
                   indented
               )(lmrFromStrings(
                   intercalate(
                       blnCompact ? [] : ['│'],
                       [treeFix(' ', '┌', '│')(lmrs[0])]
                       .concat(init(lmrs.slice(1)).map(
                           treeFix('│', '├', '│')
                       ))
                       .concat([treeFix('│', '└', ' ')(
                           lmrs[lmrs.length - 1]
                       )])
                   )
               ));
           })();
       };
       const
           measuredTree = fmapTree(
               v => {
                   const s = ' ' + v + ' ';
                   return Tuple(s.length, s)
               }, tree
           ),
           levelWidths = init(levels(measuredTree))
           .reduce(
               (a, level) => a.concat(maximum(level.map(fst))),
               []
           ),
           treeLines = stringsFromLMR(
               levelWidths.reduceRight(
                   lmrBuild, x => x
               )(measuredTree)
           );
       return unlines(
           blnPruned ? (
               treeLines.filter(
                   s => s.split()
                   .some(c => !' │'.includes(c))
               )
           ) : treeLines
       );
   };

   // TESTS ----------------------------------------------
   const main = () => {

       // tree :: Tree String
       const tree = Node(
           'Alpha', [
               Node('Beta', [
                   Node('Epsilon', []),
                   Node('Zeta', []),
                   Node('Eta', [])
               ]),
               Node('Gamma', [Node('Theta', [])]),
               Node('Delta', [
                   Node('Iota', []),
                   Node('Kappa', []),
                   Node('Lambda', [])
               ])
           ]);

       // tree2 :: Tree Int
       const tree2 = Node(
           1,
           [
               Node(2, [
                   Node(4, []),
                   Node(5, [Node(7, [])])
               ]),
               Node(3, [
                   Node(6, [
                       Node(8, []),
                       Node(9, [])
                   ])
               ])
           ]
       );

       // strTrees :: String
       const strTrees = ([
           'Compacted (parents not all vertically centered):',
           drawTree2(true)(false)(tree2),
           'Fully expanded, with vertical centering:',
           drawTree2(false)(false)(tree),
           'Vertically centered, with nodeless lines pruned out:',
           drawTree2(false)(true)(tree),
       ].join('\n\n'));

       return (
           console.log(strTrees),
           strTrees
       );
   };

   // GENERIC FUNCTIONS ----------------------------------

   // Node :: a -> [Tree a] -> Tree a
   const Node = (v, xs) => ({
       type: 'Node',
       root: v, // any type of value (consistent across tree)
       nest: xs || []
   });

   // Tuple (,) :: a -> b -> (a, b)
   const Tuple = (a, b) => ({
       type: 'Tuple',
       '0': a,
       '1': b,
       length: 2
   });

   // Tuple3 (,,) :: a -> b -> c -> (a, b, c)
   const Tuple3 = (a, b, c) => ({
       type: 'Tuple3',
       '0': a,
       '1': b,
       '2': c,
       length: 3
   });

   // compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
   const compose = (f, g) => x => f(g(x));

   // concat :: a -> [a]
   // concat :: [String] -> String
   const concat = xs =>
       0 < xs.length ? (() => {
           const unit = 'string' !== typeof xs[0] ? (
               []
           ) : ;
           return unit.concat.apply(unit, xs);
       })() : [];

   // fmapTree :: (a -> b) -> Tree a -> Tree b
   const fmapTree = (f, tree) => {
       const go = node => Node(
           f(node.root),
           node.nest.map(go)
       );
       return go(tree);
   };

   // fst :: (a, b) -> a
   const fst = tpl => tpl[0];

   // identity :: a -> a
   const identity = x => x;

   // init :: [a] -> [a]
   const init = xs =>
       0 < xs.length ? (
           xs.slice(0, -1)
       ) : undefined;

   // intercalate :: [a] -> a -> [a]
   // intercalate :: String -> [String] -> String
   const intercalate = (sep, xs) =>
       0 < xs.length && 'string' === typeof sep &&
       'string' === typeof xs[0] ? (
           xs.join(sep)
       ) : concat(intersperse(sep, xs));

   // intersperse(0, [1,2,3]) -> [1, 0, 2, 0, 3]

   // intersperse :: a -> [a] -> [a]
   // intersperse :: Char -> String -> String
   const intersperse = (sep, xs) => {
       const bln = 'string' === typeof xs;
       return xs.length > 1 ? (
           (bln ? concat : x => x)(
               (bln ? (
                   xs.split()
               ) : xs)
               .slice(1)
               .reduce((a, x) => a.concat([sep, x]), [xs[0]])
           )) : xs;
   };

   // iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a]
   const iterateUntil = (p, f, x) => {
       const vs = [x];
       let h = x;
       while (!p(h))(h = f(h), vs.push(h));
       return vs;
   };

   // Returns Infinity over objects without finite length.
   // This enables zip and zipWith to choose the shorter
   // argument when one is non-finite, like cycle, repeat etc

   // length :: [a] -> Int
   const length = xs =>
       (Array.isArray(xs) || 'string' === typeof xs) ? (
           xs.length
       ) : Infinity;

   // levels :: Tree a -> a
   const levels = tree =>
       iterateUntil(
           xs => 1 > xs.length,
           ys => [].concat(...ys.map(nest)),
           [tree]
       ).map(xs => xs.map(root));

   // maximum :: Ord a => [a] -> a
   const maximum = xs =>
       0 < xs.length ? (
           xs.slice(1).reduce((a, x) => x > a ? x : a, xs[0])
       ) : undefined;

   // nest :: Tree a -> [a]
   const nest = tree => tree.nest;

   // root :: Tree a -> a
   const root = tree => tree.root;

   // splitAt :: Int -> [a] -> ([a], [a])
   const splitAt = (n, xs) =>
       Tuple(xs.slice(0, n), xs.slice(n));

   // unlines :: [String] -> String
   const unlines = xs => xs.join('\n');

   // MAIN ---
   return main();

})();</lang>

Output:

Compacted (parents not all vertically centered):

       ┌ 4 
   ┌ 2 ┴ 5 ─ 7 
 1 ┤       ┌ 8 
   └ 3 ─ 6 ┴ 9 

Fully expanded, with vertical centering:

               ┌ Epsilon 
               │
       ┌─ Beta ┼─── Zeta 
       │       │
       │       └──── Eta 
       │
 Alpha ┼ Gamma ─── Theta 
       │
       │       ┌─── Iota 
       │       │
       └ Delta ┼── Kappa 
               │
               └─ Lambda 

Vertically centered, with nodeless lines pruned out:

               ┌ Epsilon 
       ┌─ Beta ┼─── Zeta 
       │       └──── Eta 
 Alpha ┼ Gamma ─── Theta 
       │       ┌─── Iota 
       └ Delta ┼── Kappa 
               └─ Lambda

Decorated outline

<lang JavaScript>(() => {

   'use strict';

   // drawTree :: Bool -> Tree String -> String
   const drawTree = blnCompact => tree => {
       // Simple decorated-outline style of ascii tree drawing,
       // with nodeless lines pruned out if blnCompact is True.
       const xs = draw(tree);
       return unlines(
           blnCompact ? (
               xs.filter(
                   s => s.split()
                   .some(c => !' │'.includes(c))
               )
           ) : xs
       );
   };

   // draw :: Tree String -> [String]
   const draw = node => {
       // shift :: String -> String -> [String] -> [String]
       const shift = (first, other, xs) =>
           zipWith(
               append,
               cons(first, replicate(xs.length - 1, other)),
               xs
           );
       // drawSubTrees :: [Tree String] -> [String]
       const drawSubTrees = xs => {
           const lng = xs.length;
           return 0 < lng ? (
               1 < lng ? append(
                   cons(
                       '│',
                       shift('├─ ', '│  ', draw(xs[0]))
                   ),
                   drawSubTrees(xs.slice(1))
               ) : cons('│', shift('└─ ', '   ', draw(xs[0])))
           ) : [];
       };
       return append(
           lines(node.root.toString()),
           drawSubTrees(node.nest)
       );
   };

   // TEST -----------------------------------------------
   const main = () => {
       const tree = Node(
           'Alpha', [
               Node('Beta', [
                   Node('Epsilon', []),
                   Node('Zeta', []),
                   Node('Eta', [])
               ]),
               Node('Gamma', [Node('Theta', [])]),
               Node('Delta', [
                   Node('Iota', []),
                   Node('Kappa', []),
                   Node('Lambda', [])
               ])
           ]);

       return [true, false]
       .map(blnCompact => drawTree(blnCompact)(tree))
       .join('\n\n');
   };

   // GENERIC FUNCTIONS ----------------------------------

   // Node :: a -> [Tree a] -> Tree a
   const Node = (v, xs) => ({
       type: 'Node',
       root: v, // any type of value (consistent across tree)
       nest: xs || []
   });

   // append (++) :: [a] -> [a] -> [a]
   // append (++) :: String -> String -> String
   const append = (xs, ys) => xs.concat(ys);

   // chars :: String -> [Char]
   const chars = s => s.split();

   // cons :: a -> [a] -> [a]
   const cons = (x, xs) => [x].concat(xs);

   // Returns Infinity over objects without finite length.
   // This enables zip and zipWith to choose the shorter
   // argument when one is non-finite, like cycle, repeat etc

   // length :: [a] -> Int
   const length = xs =>
       (Array.isArray(xs) || 'string' === typeof xs) ? (
           xs.length
       ) : Infinity;

   // lines :: String -> [String]
   const lines = s => s.split(/[\r\n]/);

   // replicate :: Int -> a -> [a]
   const replicate = (n, x) =>
       Array.from({
           length: n
       }, () => x);

   // take :: Int -> [a] -> [a]
   const take = (n, xs) =>
       xs.slice(0, n);

   // unlines :: [String] -> String
   const unlines = xs => xs.join('\n');

   // Use of `take` and `length` here allows zipping with non-finite lists
   // i.e. generators like cycle, repeat, iterate.

   // zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
   const zipWith = (f, xs, ys) => {
       const
           lng = Math.min(length(xs), length(ys)),
           as = take(lng, xs),
           bs = take(lng, ys);
       return Array.from({
           length: lng
       }, (_, i) => f(as[i], bs[i], i));
   };

   // MAIN ---
   return main();

})();</lang>

Output:

Alpha
├─ Beta
│  ├─ Epsilon
│  ├─ Zeta
│  └─ Eta
├─ Gamma
│  └─ Theta
└─ Delta
   ├─ Iota
   ├─ Kappa
   └─ Lambda

Alpha
│
├─ Beta
│  │
│  ├─ Epsilon
│  │
│  ├─ Zeta
│  │
│  └─ Eta
│
├─ Gamma
│  │
│  └─ Theta
│
└─ Delta
   │
   ├─ Iota
   │
   ├─ Kappa
   │
   └─ Lambda

jq

Works with: jq

Works with gojq, the Go implementation of jq

In this entry, a tree $t is represented by an array [root, child1, child2 ...] where root must be present and cannot be an array, and the children, which may also be trees, may all be absent.

The tree [0, 1, 2, 3] is displayed as:

0
├─ 1
├─ 2
└─ 3

<lang jq># Input: an array representing a tree

Output: a stream of strings representing the tree
In this implementation, empty arrays in the tree are simply ignored.

def printTree:

 def tidy:
   sub("└─"; "  ")

") ;

 # Input: a string prefix
 def print($tree):
   if $tree|type != "array" then . + ($tree|tostring)
   else # ignore empty arrays
   ($tree | map(select(if type == "array" then length>0 else true end))) as $tree

length == 0 then empty

     elif $tree|length == 1
     then print($tree[0])
     else print($tree[0]),
          ($tree[1:] as $children

tidy as $p

print($children[:-1][]))),

              ($p + ( "└─" | print($children[-1]))) )
     end
   end ;

 . as $tree

print($tree) ;</lang>

Examples <lang jq>def bigTree:

 ["a",
  ["aa",
   ["aaa",
    ["aaaa"],
    ["aaab",
     ["aaaba"],
     ["aaabb"]],
    ["aaac"]]],
  ["ab"],
  ["ac",
   ["aca"],
   ["acb"],
   ["acc"]]] ;

[0, 1, 2, 3], [1,[2,3,[4, 5, [6,7,8], 9, [10,11]]]], bigTree

("Tree with array representation:\n\(.)\n",

 printTree,
 "")</lang>

Output:

Tree with array representation:
[0,1,2,3]

0
├─1
├─2
└─3

Tree with array representation:
[1,[2,3,[4,5,[6,7,8],9,[10,11]]]]

1
└─2
  ├─3
  └─4
    ├─5
    ├─6
    | ├─7
    | └─8
    ├─9
    └─10
      └─11

Tree with array representation:
["a",["aa",["aaa",["aaaa"],["aaab",["aaaba"],["aaabb"]],["aaac"]]],["ab"],["ac",["aca"],["acb"],["acc"]]]

a
├─aa
| └─aaa
|   ├─aaaa
|   ├─aaab
|   | ├─aaaba
|   | └─aaabb
|   └─aaac
├─ab
└─ac
  ├─aca
  ├─acb
  └─acc

Julia

Run from Julia REPL. <lang Julia>using Gadfly, LightGraphs, GraphPlot

gx = kronecker(5, 12, 0.57, 0.19, 0.19) gplot(gx) </lang>

Kotlin

Translation of: C

<lang scala>// version 1.2.0

import java.util.Random

class Stem(var str: String? = null, var next: Stem? = null)

const val SDOWN = " |" const val SLAST = " `" const val SNONE = " "

val rand = Random()

fun tree(root: Int, head: Stem?) {

   val col = Stem()
   var head2 = head
   var tail = head
   while (tail != null) {
       print(tail.str)
       if (tail.next == null) break
       tail = tail.next
   }
   println("--$root")
   if (root <= 1) return
   if (tail != null && tail.str == SLAST) tail.str = SNONE
   if (tail == null) {
       head2 = col
       tail = head2
   }
   else {
       tail.next = col
   }
   var root2 = root
   while (root2 != 0) { // make a tree by doing something random
       val r = 1 + rand.nextInt(root2)
       root2 -= r
       col.str = if (root2 != 0) SDOWN else SLAST
       tree(r, head2)
   }
   tail.next = null

}

fun main(args: Array<String>) {

   val n = 8
   tree(n, null)

}</lang>

Sample output (unlike the C entry, should be different each time it's run):

--8
  |--7
  |  |--6
  |  |  |--5
  |  |  |  |--3
  |  |  |  |  |--2
  |  |  |  |  |  |--1
  |  |  |  |  |  `--1
  |  |  |  |  `--1
  |  |  |  `--2
  |  |  |     `--2
  |  |  |        |--1
  |  |  |        `--1
  |  |  `--1
  |  `--1
  `--1

Lingo

<lang lingo>-- parent script "TreeItem" -- (minimal implementation with direct property access)

property name property children

on new (me, itemName)

 me.name = itemName
 me.children = []
 return me

end

on addChild (me, child)

 me.children.add(child)

end

-- print a tree on printTree (me, treeItem, indent)

 if voidP(treeItem) then treeItem = me
 if voidP(indent) then indent = ""
 put indent&treeItem.name
 repeat with c in treeItem.children
   me.printTree(c, indent&"  ")
 end repeat

end</lang> Usage: <lang lingo>-- create a tree root = script("TreeItem").new("root") a = script("TreeItem").new("a") root.addChild(a) b = script("TreeItem").new("b") root.addChild(b) a1 = script("TreeItem").new("a1") a.addChild(a1) a11 = script("TreeItem").new("a11") a1.addChild(a11) a12 = script("TreeItem").new("a12") a1.addChild(a12) b1 = script("TreeItem").new("b1") b.addChild(b1)

-- print the tree root.printTree()</lang>

Output:

-- "root"
-- "  a"
-- "    a1"
-- "      a11"
-- "      a12"
-- "  b"
-- "    b1"

Lua

Translation of: C#

<lang lua>function makeTree(v,ac)

   if type(ac) == "table" then
       return {value=v,children=ac}
   else
       return {value=v}
   end

end

function printTree(t,last,prefix)

   if last == nil then
       printTree(t, false, )
   else
       local current = 
       local next =

       if last then
           current = prefix .. '\\-' .. t.value
           next = prefix .. '  '
       else
           current = prefix .. '|-' .. t.value
           next = prefix .. '| '
       end

       print(current:sub(3))
       if t.children ~= nil then
           for k,v in pairs(t.children) do
               printTree(v, k == #t.children, next)
           end
       end
   end

end

printTree(

   makeTree('A', {
       makeTree('B0', {
           makeTree('C1'),
           makeTree('C2', {
               makeTree('D', {
                   makeTree('E1'),
                   makeTree('E2'),
                   makeTree('E3')
               })
           }),
           makeTree('C3', {
               makeTree('F1'),
               makeTree('F2'),
               makeTree('F3', {makeTree('G')}),
               makeTree('F4', {
                   makeTree('H1'),
                   makeTree('H2')
               })
           })
       }),
       makeTree('B1',{
           makeTree('K1'),
           makeTree('K2', {
               makeTree('L1', {makeTree('M')}),
               makeTree('L2'),
               makeTree('L3')
           }),
           makeTree('K3')
       })
   })

)</lang>

Output:

A
|-B0
| |-C1
| |-C2
| | \-D
| |   |-E1
| |   |-E2
| |   \-E3
| \-C3
|   |-F1
|   |-F2
|   |-F3
|   | \-G
|   \-F4
|     |-H1
|     \-H2
\-B1
  |-K1
  |-K2
  | |-L1
  | | \-M
  | |-L2
  | \-L3
  \-K3

Maple

<lang Maple>T := GraphTheory:-Graph([1, 2, 3, 4, 5], {{1, 2}, {2, 3}, {2, 4}, {4, 5}}): GraphTheory:-DrawGraph(T, style = tree);</lang>

Mathematica/Wolfram Language

Tree graph

Make a tree graph. In Mathematica, \[DirectedEdge] will appear as an arrow in the code.

<lang Mathematica>edges = {1 \[DirectedEdge] 2, 1 \[DirectedEdge] 3, 2 \[DirectedEdge] 4, 2 \[DirectedEdge] 5,

             3 \[DirectedEdge] 6, 4 \[DirectedEdge] 7};

t = TreeGraph[edges, GraphStyle -> "VintageDiagram"]</lang>

Show the syntactical structure of the above code. Defer is added to impede TreeGraph from becoming a graphical object.

<lang Mathematica>TreeForm[Defer@

 TreeGraph[{1 \[DirectedEdge] 2, 1 \[DirectedEdge] 3, 2 \[DirectedEdge] 4, 2 \[DirectedEdge] 5, 
  3 \[DirectedEdge] 6,  4 \[DirectedEdge] 7}, VertexLabels -> "Name"]]</lang>

Opener view

Here's another way to display a tree. The triangles open/close when clicked on.

<lang Mathematica>OpenerView[{1, Column@{OpenerView[{2, Column@{OpenerView[{4, 7}, True], 5}}, True],

    OpenerView[{3,  OpenerView[{TraditionalForm[Cos[x]], Plot[Cos[x], {x, 0, 10}, ImageSize -> 150]}, 
    True]}, True]}}, True]</lang>

File:Opener.jpg

Maxima

<lang maxima>load(graphs)$

g: random_tree(10)$

is_tree(g); true

draw_graph(g)$</lang>

Nim

Translation of: Haskell

<lang nim>import strutils

type

 Node[T] = ref object
   data: T
   left, right: Node[T]

proc n[T](data: T; left, right: Node[T] = nil): Node[T] =

 Node[T](data: data, left: left, right: right)

proc indent[T](n: Node[T]): seq[string] =

 if n == nil: return @["-- (null)"]

 result = @["--" & $n.data]

 for a in indent n.left: result.add "  |" & a

 let r = indent n.right
 result.add "  `" & r[0]
 for a in r[1..r.high]: result.add "   " & a

let tree = 1.n(2.n(4.n(7.n),5.n),3.n(6.n(8.n,9.n)))

echo tree.indent.join("\n")</lang>

Output:

--1
  |--2
  |  |--4
  |  |  |--7
  |  |  |  |-- (null)
  |  |  |  `-- (null)
  |  |  `-- (null)
  |  `--5
  |     |-- (null)
  |     `-- (null)
  `--3
     |--6
     |  |--8
     |  |  |-- (null)
     |  |  `-- (null)
     |  `--9
     |     |-- (null)
     |     `-- (null)
     `-- (null)

Perl

<lang perl>#!/usr/bin/perl use warnings; use strict; use utf8; use open OUT => ':utf8', ':std';

sub parse {

   my ($tree) = shift;
   if (my ($root, $children) = $tree =~ /^(.+?)\((.*)\)$/) {

       my $depth = 0;
       for my $pos (0 .. length($children) - 1) {
           my $char = \substr $children, $pos, 1;
           if (0 == $depth and ',' eq $$char) {
               $$char = "\x0";
           } elsif ('(' eq $$char) {
               $depth++;
           } elsif (')' eq $$char) {
               $depth--;
           }
       }
       return($root, [map parse($_), split /\x0/, $children]);

   } else { # Leaf.
       return $tree;
   }

}

sub output {

   my ($parsed, $prefix) = @_;
   my $is_root = not defined $prefix;
   $prefix //= ' ';
   while (my $member = shift @$parsed) {
       my $last = !@$parsed || (1 == @$parsed and ref $parsed->[0]);
       unless ($is_root) {
           substr $prefix, -3, 1, ' ';
           substr($prefix, -4, 1) =~ s/├/│/;
           substr $prefix, -2, 1, ref $member ? ' ' : '└' if $last;
       }

       if (ref $member) {
           output($member, $prefix . '├─');
       } else {
           print $prefix, $member, "\n";
       }
   }

}

my $tree = 'a(b0(c1,c2(d(ef,gh)),c3(i1,i2,i3(jj),i4(kk,m))),b1(C1,C2(D1(E),D2,D3),C3))'; my $parsed = [parse($tree)]; output($parsed);</lang>

Output:

 a
 ├─b0
 │ ├─c1
 │ ├─c2
 │ │ └─d
 │ │   ├─ef
 │ │   └─gh
 │ └─c3
 │   ├─i1
 │   ├─i2
 │   ├─i3
 │   │ └─jj
 │   └─i4
 │     ├─kk
 │     └─m
 └─b1
   ├─C1
   ├─C2
   │ ├─D1
   │ │ └─E
   │ ├─D2
   │ └─D3
   └─C3

Phix

function rand_tree(integer low, integer high)
    for i=1 to 2 do
        integer v = rand(high-low+1)-1+low
        if v!=low
        and v!=high then
            return {v,rand_tree(low,v),rand_tree(v,high)}
        end if
    end for
    return 0
end function
 
object tree = rand_tree(0,20)   -- (can be 0, ~1% chance)
 
constant Horizontal = #C4,
         Horizontals = "\#C4",
         TopLeft = #DA,
         Vertical = #B3,
         BtmLeft = #C0
 
procedure visualise_tree(object tree, string root=Horizontals)
    if atom(tree) then
        puts(1,"<empty>\n")
    else
        object {v,l,r} = tree
        integer g = root[$]
        if sequence(l) then
            root[$] = iff(g=TopLeft or g=Horizontal?' ':Vertical)
            visualise_tree(l,root&TopLeft)
        end if
        root[$] = g
        puts(1,root)
        ?v
        if sequence(r) then
            root[$] = iff(g=TopLeft?Vertical:' ')
            visualise_tree(r,root&BtmLeft)
        end if
    end if
end procedure
 
visualise_tree(tree)

Output:

   ┌3
   │└4
   │ └5
  ┌7
 ┌9
 │└10
 │ └11
─12
 │ ┌13
 │┌14
 └15
  │ ┌16
  │┌17
  ││└18
  └19

A much simpler but less aesthetically pleasing way is just

pp(tree,{pp_Nest,10})

Output:

{1,
 0,
 {5,
  0,
  {9,
   {8,
    {6,
     0,
     0},
    0},
   0}}}

PicoLisp

'view' is a built-in function in PicoLisp.

Output:

+-- 1
|
+---+-- 2
|   |
|   +---+-- 3
|   |   |
|   |   +---+-- 4
|   |   |
|   |   +---+-- 5
|   |   |
|   |   +---+-- 6
|   |       |
|   |       +---+-- 7
|   |
|   +---+-- 8
|   |   |
|   |   +---+-- 9
|   |
|   +---+-- 10
|
+---+-- 11
    |
    +---+-- 12
    |
    +---+-- 13

Prolog

XPCE

XPCE is the SWI-Prolog native GUI library. <lang prolog>% direction may be horizontal/vertical/list display_tree(Direction) :- sformat(A, 'Display tree ~w', [Direction]), new(D, window(A)), send(D, size, size(350,200)), new(T, tree(text('Root'))), send(T, neighbour_gap, 10), new(S1, node(text('Child1'))), new(S2, node(text('Child2'))), send_list(T, son,[S1,S2]), new(S11, node(text('Grandchild1'))), new(S12, node(text('Grandchild2'))), send_list(S1, son, [S11, S12]), new(S21, node(text('Grandchild3'))), new(S22, node(text('Grandchild4'))), send_list(S2, son, [S21, S22]), send(T, direction, Direction), send(D, display, T), send(D, open). </lang>

Python

Library module

Python has the pprint module for pretty-printing data.

If you set the presumed width of the output to 1 then pprint will print each level of a nested tuple (which is Pythons obvious method of creating a tree), on a separate line: <lang python>Python 3.2.3 (default, May 3 2012, 15:54:42) [GCC 4.6.3] on linux2 Type "copyright", "credits" or "license()" for more information. >>> help('pprint.pprint') Help on function pprint in pprint:

pprint.pprint = pprint(object, stream=None, indent=1, width=80, depth=None)

   Pretty-print a Python object to a stream [default is sys.stdout].

>>> from pprint import pprint >>> for tree in [ (1, 2, 3, 4, 5, 6, 7, 8), (1, (( 2, 3 ), (4, (5, ((6, 7), 8))))), ((((1, 2), 3), 4), 5, 6, 7, 8) ]: print("\nTree %r can be pprint'd as:" % (tree, )) pprint(tree, indent=1, width=1)

Tree (1, 2, 3, 4, 5, 6, 7, 8) can be pprint'd as: (1,

2,
3,
4,
5,
6,
7,
8)

Tree (1, ((2, 3), (4, (5, ((6, 7), 8))))) can be pprint'd as: (1,

((2,
  3),
 (4,
  (5,
   ((6,
     7),
    8)))))

Tree ((((1, 2), 3), 4), 5, 6, 7, 8) can be pprint'd as: ((((1,

   2),
  3),
 4),
5,
6,
7,
8)

>>> </lang>

pprint (and print), prints Pythons standard container types in a format that is valid python so Python could parse its output: <lang python>>>> tree = "a",("b0",("c1","c2",("d",("ef","gh")),"c3",("i1","i2","i3",("jj"),"i4",("kk","m"))),"b1",("C1","C2",("D1",("E"),"D2","D3"),"C3")) >>> pprint(tree, width=1) ('a',

('b0',
 ('c1',
  'c2',
  ('d',
   ('ef',
    'gh')),
  'c3',
  ('i1',
   'i2',
   'i3',
   'jj',
   'i4',
   ('kk',
    'm'))),
 'b1',
 ('C1',
  'C2',
  ('D1',
   'E',
   'D2',
   'D3'),
  'C3')))

>>> copypasteoutput = ('a', ... ('b0', ... ('c1', ... 'c2', ... ('d', ... ('ef', ... 'gh')), ... 'c3', ... ('i1', ... 'i2', ... 'i3', ... 'jj', ... 'i4', ... ('kk', ... 'm'))), ... 'b1', ... ('C1', ... 'C2', ... ('D1', ... 'E', ... 'D2', ... 'D3'), ... 'C3'))) >>> tree == copypasteoutput True >>> </lang>

pprints width parameter allows it to fold some structure to better fit the page: <lang python>>>> pprint(tree, width=60) ('a',

('b0',
 ('c1',
  'c2',
  ('d', ('ef', 'gh')),
  'c3',
  ('i1', 'i2', 'i3', 'jj', 'i4', ('kk', 'm'))),
 'b1',
 ('C1', 'C2', ('D1', 'E', 'D2', 'D3'), 'C3')))

>>> </lang>

pprint works with with a mix of nested container types. Here we create a tree from both lists and tuples: <lang python>>>> mixedtree = ['a', ('b0', ('c1', 'c2', ['d', ('ef', 'gh')], 'c3', ('i1', 'i2', ... 'i3', 'jj', 'i4', ['kk', 'm'])), 'b1', ('C1', 'C2', ('D1', 'E', ... 'D2', 'D3'), 'C3'))] >>> pprint(mixedtree, width=1) ['a',

('b0',
 ('c1',
  'c2',
  ['d',
   ('ef',
    'gh')],
  'c3',
  ('i1',
   'i2',
   'i3',
   'jj',
   'i4',
   ['kk',
    'm'])),
 'b1',
 ('C1',
  'C2',
  ('D1',
   'E',
   'D2',
   'D3'),
  'C3'))]

>>> pprint(mixedtree, width=60) ['a',

('b0',
 ('c1',
  'c2',
  ['d', ('ef', 'gh')],
  'c3',
  ('i1', 'i2', 'i3', 'jj', 'i4', ['kk', 'm'])),
 'b1',
 ('C1', 'C2', ('D1', 'E', 'D2', 'D3'), 'C3'))]

>>> </lang>

Functional composition

Vertically centered parents

Using the same tree structure (including tree node constructor and accessors) as in the Tree Traversal task, and centering parent nodes vertically:

Works with: Python version 3

<lang python>Textually visualized tree, with vertically-centered parent nodes

from functools import reduce from itertools import (chain, takewhile)

              ┌ Epsilon
              ├─── Zeta
      ┌─ Beta ┼──── Eta
      │       │         ┌───── Mu
      │       └── Theta ┤
Alpha ┤                 └───── Nu
      ├ Gamma ────── Xi ─ Omicron
      │       ┌─── Iota
      └ Delta ┼── Kappa
              └─ Lambda

Tree style and algorithm inspired by the Haskell snippet at:
https://doisinkidney.com/snippets/drawing-trees.html

drawTree2 :: Bool -> Bool -> Tree a -> String

def drawTree2(blnCompact):

   Monospaced UTF8 left-to-right text tree in a
      compact or expanded format, with any lines
      containing no nodes optionally pruned out.
   
   def go(blnPruned, tree):
       # measured :: a -> (Int, String)
       def measured(x):
           Value of a tree node
              tupled with string length.
           
           s = ' ' + str(x) + ' '
           return len(s), s

       # lmrFromStrings :: [String] -> ([String], String, [String])
       def lmrFromStrings(xs):
           Lefts, Mid, Rights.
           i = len(xs) // 2
           ls, rs = xs[0:i], xs[i:]
           return ls, rs[0], rs[1:]

       # stringsFromLMR :: ([String], String, [String]) -> [String]
       def stringsFromLMR(lmr):
           ls, m, rs = lmr
           return ls + [m] + rs

       # fghOverLMR
       # :: (String -> String)
       # -> (String -> String)
       # -> (String -> String)
       # -> ([String], String, [String])
       # -> ([String], String, [String])
       def fghOverLMR(f, g, h):
           def go(lmr):
               ls, m, rs = lmr
               return (
                   [f(x) for x in ls],
                   g(m),
                   [h(x) for x in rs]
               )
           return lambda lmr: go(lmr)

       # leftPad :: Int -> String -> String
       def leftPad(n):
           return lambda s: (' ' * n) + s

       # treeFix :: (Char, Char, Char) -> ([String], String, [String])
       #                               ->  [String]
       def treeFix(l, m, r):
           def cfix(x):
               return lambda xs: x + xs
           return compose(stringsFromLMR)(
               fghOverLMR(cfix(l), cfix(m), cfix(r))
           )

       def lmrBuild(w, f):
           def go(wsTree):
               nChars, x = wsTree['root']
               _x = ('─' * (w - nChars)) + x
               xs = wsTree['nest']
               lng = len(xs)

               # linked :: String -> String
               def linked(s):
                   c = s[0]
                   t = s[1:]
                   return _x + '┬' + t if '┌' == c else (
                       _x + '┤' + t if '│' == c else (
                           _x + '┼' + t if '├' == c else (
                               _x + '┴' + t
                           )
                       )
                   )

               # LEAF ------------------------------------
               if 0 == lng:
                   return ([], _x, [])

               # SINGLE CHILD ----------------------------
               elif 1 == lng:
                   def lineLinked(z):
                       return _x + '─' + z
                   rightAligned = leftPad(1 + w)
                   return fghOverLMR(
                       rightAligned,
                       lineLinked,
                       rightAligned
                   )(f(xs[0]))

               # CHILDREN --------------------------------
               else:
                   rightAligned = leftPad(w)
                   lmrs = [f(x) for x in xs]
                   return fghOverLMR(
                       rightAligned,
                       linked,
                       rightAligned
                   )(
                       lmrFromStrings(
                           intercalate([] if blnCompact else ['│'])(
                               [treeFix(' ', '┌', '│')(lmrs[0])] + [
                                   treeFix('│', '├', '│')(x) for x
                                   in lmrs[1:-1]
                               ] + [treeFix('│', '└', ' ')(lmrs[-1])]
                           )
                       )
                   )
           return lambda wsTree: go(wsTree)

       measuredTree = fmapTree(measured)(tree)
       levelWidths = reduce(
           lambda a, xs: a + [max(x[0] for x in xs)],
           levels(measuredTree),
           []
       )
       treeLines = stringsFromLMR(
           foldr(lmrBuild)(None)(levelWidths)(
               measuredTree
           )
       )
       return [
           s for s in treeLines
           if any(c not in '│ ' for c in s)
       ] if (not blnCompact and blnPruned) else treeLines

   return lambda blnPruned: (
       lambda tree: '\n'.join(go(blnPruned, tree))
   )

TEST ----------------------------------------------------
main :: IO ()

def main():

   Trees drawn in varying formats

   # tree1 :: Tree Int
   tree1 = Node(1)([
       Node(2)([
           Node(4)([
               Node(7)([])
           ]),
           Node(5)([])
       ]),
       Node(3)([
           Node(6)([
               Node(8)([]),
               Node(9)([])
           ])
       ])
   ])

   # tree :: Tree String
   tree2 = Node('Alpha')([
       Node('Beta')([
           Node('Epsilon')([]),
           Node('Zeta')([]),
           Node('Eta')([]),
           Node('Theta')([
               Node('Mu')([]),
               Node('Nu')([])
           ])
       ]),
       Node('Gamma')([
           Node('Xi')([Node('Omicron')([])])
       ]),
       Node('Delta')([
           Node('Iota')([]),
           Node('Kappa')([]),
           Node('Lambda')([])
       ])
   ])

   print(
       '\n\n'.join([
           'Fully compacted (parents not all centered):',
           drawTree2(True)(False)(
               tree1
           ),
           'Expanded with vertically centered parents:',
           drawTree2(False)(False)(
               tree2
           ),
           'Centered parents with nodeless lines pruned out:',
           drawTree2(False)(True)(
               tree2
           )
       ])
   )

GENERIC -------------------------------------------------

Node :: a -> [Tree a] -> Tree a

def Node(v):

   Contructor for a Tree node which connects a
      value of some kind to a list of zero or
      more child trees.
   
   return lambda xs: {'type': 'Tree', 'root': v, 'nest': xs}

compose (<<<) :: (b -> c) -> (a -> b) -> a -> c

def compose(g):

   Right to left function composition.
   return lambda f: lambda x: g(f(x))

concatMap :: (a -> [b]) -> [a] -> [b]

def concatMap(f):

   A concatenated list over which a function has been mapped.
      The list monad can be derived by using a function f which
      wraps its output in a list,
      (using an empty list to represent computational failure).
   
   return lambda xs: list(
       chain.from_iterable(map(f, xs))
   )

fmapTree :: (a -> b) -> Tree a -> Tree b

def fmapTree(f):

   A new tree holding the results of
      applying f to each root in
      the existing tree.
   
   def go(x):
       return Node(f(x['root']))(
           [go(v) for v in x['nest']]
       )
   return lambda tree: go(tree)

foldr :: (a -> b -> b) -> b -> [a] -> b

def foldr(f):

   Right to left reduction of a list,
      using the binary operator f, and
      starting with an initial accumulator value.
   
   def g(x, a):
       return f(a, x)
   return lambda acc: lambda xs: reduce(
       g, xs[::-1], acc
   )

intercalate :: [a] -> a -> [a]
intercalate :: String -> [String] -> String

def intercalate(x):

   The concatenation of xs
      interspersed with copies of x.
   
   return lambda xs: x.join(xs) if isinstance(x, str) else list(
       chain.from_iterable(
           reduce(lambda a, v: a + [x, v], xs[1:], [xs[0]])
       )
   ) if xs else []

iterate :: (a -> a) -> a -> Gen [a]

def iterate(f):

   An infinite list of repeated
      applications of f to x.
   
   def go(x):
       v = x
       while True:
           yield v
           v = f(v)
   return lambda x: go(x)

levels :: Tree a -> a

def levels(tree):

   A list of the nodes at each level of the tree.
   return list(
       map_(map_(root))(
           takewhile(
               bool,
               iterate(concatMap(nest))(
                   [tree]
               )
           )
       )
   )

map :: (a -> b) -> [a] -> [b]

def map_(f):

   The list obtained by applying f
      to each element of xs.
   
   return lambda xs: list(map(f, xs))

nest :: Tree a -> [Tree a]

def nest(t):

   Accessor function for children of tree node.
   return t['nest'] if 'nest' in t else None

root :: Tree a -> a

def root(t):

   Accessor function for data of tree node.
   return t['root'] if 'root' in t else None

MAIN ---

if __name__ == '__main__':

   main()</lang>

Output:

Fully compacted (parents not all centered):

       ┌ 4 ─ 7 
   ┌ 2 ┴ 5 
 1 ┤       ┌ 8 
   └ 3 ─ 6 ┴ 9 

Expanded with vertically centered parents:

               ┌ Epsilon 
               │
               ├─── Zeta 
               │
       ┌─ Beta ┼──── Eta 
       │       │
       │       │         ┌───── Mu 
       │       └── Theta ┤
 Alpha ┤                 └───── Nu 
       │
       ├ Gamma ────── Xi ─ Omicron 
       │
       │       ┌─── Iota 
       │       │
       └ Delta ┼── Kappa 
               │
               └─ Lambda 

Centered parents with nodeless lines pruned out:

               ┌ Epsilon 
               ├─── Zeta 
       ┌─ Beta ┼──── Eta 
       │       │         ┌───── Mu 
       │       └── Theta ┤
 Alpha ┤                 └───── Nu 
       ├ Gamma ────── Xi ─ Omicron 
       │       ┌─── Iota 
       └ Delta ┼── Kappa 
               └─ Lambda

Simple decorated-outline tree

Works with: Python version 3

<lang python>Visualize a tree

from itertools import (chain, repeat, starmap) from operator import (add)

drawTree :: Tree a -> String

def drawTree(tree):

   ASCII diagram of a tree.
   return '\n'.join(draw(tree))

draw :: Tree a -> [String]

def draw(node):

   List of the lines of an ASCII
      diagram of a tree.
   def shift(first, other, xs):
       return list(starmap(
           add,
           zip(
               chain([first], repeat(other, len(xs) - 1)),
               xs
           )
       ))

   def drawSubTrees(xs):
       return (
           (
               ['│'] + shift(
                   '├─ ', '│  ', draw(xs[0])
               ) + drawSubTrees(xs[1:])
           ) if 1 < len(xs) else ['│'] + shift(
               '└─ ', '   ', draw(xs[0])
           )
       ) if xs else []

   return (str(root(node))).splitlines() + (
       drawSubTrees(nest(node))
   )

TEST ----------------------------------------------------
main :: IO ()

def main():

   Test

   # tree :: Tree Int
   tree = Node(1)([
       Node(2)([
           Node(4)([
               Node(7)([])
           ]),
           Node(5)([])
       ]),
       Node(3)([
           Node(6)([
               Node(8)([]),
               Node(9)([])
           ])
       ])
   ])

   print(drawTree(tree))

GENERIC -------------------------------------------------

Node :: a -> [Tree a] -> Tree a

def Node(v):

   Contructor for a Tree node which connects a
      value of some kind to a list of zero or
      more child trees.
   return lambda xs: {'root': v, 'nest': xs}

nest :: Tree a -> [Tree a]

def nest(tree):

   Accessor function for children of tree node.
   return tree['nest'] if 'nest' in tree else None

root :: Dict -> a

def root(dct):

   Accessor function for data of tree node.
   return dct['root'] if 'root' in dct else None

MAIN ---

if __name__ == '__main__':

   main()</lang>

Output:

1
│
├─ 2
│  │
│  ├─ 4
│  │  │
│  │  └─ 7
│  │
│  └─ 5
│
└─ 3
   │
   └─ 6
      │
      ├─ 8
      │
      └─ 9

Racket

lang racket/base

(define (visualize t0)

 (let loop ([t t0] [last? #t] [indent '()])
   (define (I mid last) (cond [(eq? t t0) ""] [last? mid] [else last]))
   (for-each display (reverse indent))
   (unless (eq? t t0) (printf "|\n"))
   (for-each display (reverse indent))
   (printf "~a~a\n" (I "\\-" "+-") (car t))
   (for ([s (cdr t)] [n (in-range (- (length t) 2) -1 -1)])
     (loop s (zero? n) (cons (I "  " "| ") indent)))))

(visualize '(1 (2 (3 (4) (5) (6 (7))) (8 (9)) (10)) (11 (12) (13)))) </lang>

Output:

1
|
+-2
| |
| +-3
| | |
| | +-4
| | |
| | +-5
| | |
| | \-6
| |   |
| |   \-7
| |
| +-8
| | |
| | \-9
| |
| \-10
|
\-11
  |
  +-12
  |
  \-13

Raku

(formerly Perl 6)

<lang perl6>sub visualize-tree($tree, &label, &children,

                  :$indent = ,
                  :@mid = ('├─', '│ '),
                  :@end = ('└─', '  '),

) {

   sub visit($node, *@pre) {

gather {

           take @pre[0] ~ label($node);
           my @children := children($node);
           my $end = @children.end;
           for @children.kv -> $_, $child {
               when $end { take visit($child, (@pre[1] X~ @end)) }
               default   { take visit($child, (@pre[1] X~ @mid)) }
           }
       }
   }
   visit($tree, $indent xx 2);

}

example tree built up of pairs

my $tree = root=>[a=>[a1=>[a11=>[]]],b=>[b1=>[b11=>[]],b2=>[],b3=>[]]];

.map({.join("\n")}).join("\n").say for visualize-tree($tree, *.key, *.value.list);</lang>

Output:

root
├─a
│ └─a1
│   └─a11
└─b
  ├─b1
  │ └─b11
  ├─b2
  └─b3

REXX

<lang rexx>/* REXX ***************************************************************

10.05.2014 Walter Pachl using the tree and the output format of C
- - - - /

Call mktree Say node.1.0name Call tt 1, Exit

tt: Procedure Expose node. /**********************************************************************

show a subtree (recursively)
- - - - /

Parse Arg k,st
Do i=1 To node.k.0
  If i=node.k.0 Then
    s='`--'
  Else
    s='|--'
  c=node.k.i
  If st<> Then
    st=left(st,length(st)-2)'  '
  st=changestr('` ',st,'  ')
  Say st||s||node.c.0name
  Call tt c,st||s
  End
Return

Exit

mktree: Procedure Expose node. root /**********************************************************************

build the tree according to the task
- - - - /

 node.=0
 r=mknode('R');
 a=mknode('A'); Call attchild a,r
 b=mknode('B'); Call attchild b,a
 c=mknode('C'); Call attchild c,a
 d=mknode('D'); Call attchild d,b
 e=mknode('E'); Call attchild e,b
 f=mknode('F'); Call attchild f,b
 g=mknode('G'); Call attchild g,b
 h=mknode('H'); Call attchild h,d
 i=mknode('I'); Call attchild i,h
 j=mknode('J'); Call attchild j,i
 k=mknode('K'); Call attchild k,j
 l=mknode('L'); Call attchild l,j
 m=mknode('M'); Call attchild m,e
 n=mknode('N'); Call attchild n,e
 Return

mknode: Procedure Expose node. /**********************************************************************

create a new node
- - - - /

 Parse Arg name
 z=node.0+1
 node.z.0name=name
 node.0=z
 Return z                        /* number of the node just created */

attchild: Procedure Expose node. /**********************************************************************

make a the next child of father
- - - - /

 Parse Arg a,father
 node.a.0father=father
 z=node.father.0+1
 node.father.z=a
 node.father.0=z
 node.a.0level=node.father.0level+1
 Return

</lang>

Output:

R
`--A
   |--B
   |  |--D
   |  |  `--H
   |  |     `--I
   |  |        `--J
   |  |           |--K
   |  |           `--L
   |  |--E
   |  |  |--M
   |  |  `--N
   |  |--F
   |  `--G
   `--C

Ruby

Modifying Tree_traversal#Ruby by adding somewhere after the line <lang Ruby> root = BinaryTreeNode.from_array [1, [2, [4, 7], [5]], [3, [6, [8], [9]]]] </lang> the lines <lang Ruby> require 'pp' pp root </lang> will produce:

Output:

  #<BinaryTreeNode:0x804f854
   @left=
    #<BinaryTreeNode:0x804fad8
     @left=#<BinaryTreeNode:0x804fc28 @left=nil, @right=nil, @value=7>,
     @right=nil,
     @value=4>,
   @right=#<BinaryTreeNode:0x804f9c0 @left=nil, @right=nil, @value=5>,
   @value=2>,
 @right=
  #<BinaryTreeNode:0x804f074
   @left=
    #<BinaryTreeNode:0x804f218
     @left=#<BinaryTreeNode:0x804f544 @left=nil, @right=nil, @value=8>,
     @right=#<BinaryTreeNode:0x804f384 @left=nil, @right=nil, @value=9>,
     @value=6>,
   @right=nil,
   @value=3>,
 @value=1>

<lang Ruby> def ptree(tree,indent=" ")

 case tree
 when Array
   head,*tail=tree
   ptree(head,indent)
   s=tail.size-1
   tail.each_with_index { |tree1,i| ptree(tree1,"#{indent}#{((i==s) ? ' ':'|')}  ") } 
 else
    puts(indent.gsub(/\s\s$/,"--").gsub(/ --$/,"\\--")+tree.to_s)
 end

end ptree [1,2,3,[4,5,6,[7,8,9]],3,[22,33]] </lang> will produce:

Output:

--1
  |--2
  |--3
  |--4
  |  |--5
  |  |--6
  |  \--7
  |     |--8
  |     \--9
  |--3
  \--22
     \--33

Rust

Console visualization of binary trees translated from parts of the C AVL tree solution. <lang Rust> extern crate rustc_serialize; extern crate term_painter;

use rustc_serialize::json; use std::fmt::{Debug, Display, Formatter, Result}; use term_painter::ToStyle; use term_painter::Color::*;

type NodePtr = Option<usize>;

[derive(Debug, PartialEq, Clone, Copy)]

enum Side {

   Left,
   Right,
   Up,

}

[derive(Debug, PartialEq, Clone, Copy)]

enum DisplayElement {

   TrunkSpace,
   SpaceLeft,
   SpaceRight,
   SpaceSpace,
   Root,

}

impl DisplayElement {

   fn string(&self) -> String {
       match *self {
           DisplayElement::TrunkSpace => "    │   ".to_string(),
           DisplayElement::SpaceRight => "    ┌───".to_string(),
           DisplayElement::SpaceLeft => "    └───".to_string(),
           DisplayElement::SpaceSpace => "        ".to_string(),
           DisplayElement::Root => "├──".to_string(),
       }
   }

}

[derive(Debug, Clone, Copy, RustcDecodable, RustcEncodable)]

struct Node<K, V> {

   key: K,
   value: V,
   left: NodePtr,
   right: NodePtr,
   up: NodePtr,

}

impl<K: Ord + Copy, V: Copy> Node<K, V> {

   pub fn get_ptr(&self, side: Side) -> NodePtr {
       match side {
           Side::Up => self.up,
           Side::Left => self.left,
           _ => self.right,
       }
   }

}

[derive(Debug, RustcDecodable, RustcEncodable)]

struct Tree<K, V> {

   root: NodePtr,
   store: Vec<Node<K, V>>,

}

impl<K: Ord + Copy + Debug + Display, V: Debug + Copy + Display> Tree<K, V> {

   pub fn get_node(&self, np: NodePtr) -> Node<K, V> {
       assert!(np.is_some());
       self.store[np.unwrap()]
   }

   pub fn get_pointer(&self, np: NodePtr, side: Side) -> NodePtr {
       assert!(np.is_some());
       self.store[np.unwrap()].get_ptr(side)
   }

   // Prints the tree with root p.  The idea is to do an in-order traversal
   // (reverse in-order in this case, where right is on top), and print nodes as they
   // are visited, one per line. Each invocation of display() gets its own copy
   // of the display element vector e, which is grown with either whitespace or
   // a trunk element, then modified in its last and possibly second-to-last
   // characters in context.
   fn display(&self, p: NodePtr, side: Side, e: &Vec<DisplayElement>, f: &mut Formatter) {
       if p.is_none() {
           return;
       }

       let mut elems = e.clone();
       let node = self.get_node(p);
       let mut tail = DisplayElement::SpaceSpace;
       if node.up != self.root {
           // If the direction is switching, I need the trunk element to appear in the lines
           // printed before that node is visited.
           if side == Side::Left && node.right.is_some() {
               elems.push(DisplayElement::TrunkSpace);
           } else {
               elems.push(DisplayElement::SpaceSpace);
           }
       }
       let hindex = elems.len() - 1;
       self.display(node.right, Side::Right, &elems, f);

       if p == self.root {
           elems[hindex] = DisplayElement::Root;
           tail = DisplayElement::TrunkSpace;
       } else if side == Side::Right {
           // Right subtree finished
           elems[hindex] = DisplayElement::SpaceRight;
           // Prepare trunk element in case there is a left subtree
           tail = DisplayElement::TrunkSpace;
       } else if side == Side::Left {
           elems[hindex] = DisplayElement::SpaceLeft;
           let parent = self.get_node(node.up);
           if parent.up.is_some() && self.get_pointer(parent.up, Side::Right) == node.up {
               // Direction switched, need trunk element starting with this node/line
               elems[hindex - 1] = DisplayElement::TrunkSpace;
           }
       }

       // Visit node => print accumulated elements. Each node gets a line and each line gets a
       // node.
       for e in elems.clone() {
           let _ = write!(f, "{}", e.string());
       }
       let _ = write!(f,
                      "{key:>width$} ",
                      key = Green.bold().paint(node.key),
                      width = 2);
       let _ = write!(f,
                      "{value:>width$}\n",
                      value = Blue.bold().paint(format!("{:.*}", 2, node.value)),
                      width = 4);

       // Overwrite last element before continuing traversal
       elems[hindex] = tail;

       self.display(node.left, Side::Left, &elems, f);
   }

}

impl<K: Ord + Copy + Debug + Display, V: Debug + Copy + Display> Display for Tree<K, V> {

   fn fmt(&self, f: &mut Formatter) -> Result {
       if self.root.is_none() {
           write!(f, "[empty]")
       } else {
           let mut v: Vec<DisplayElement> = Vec::new();
           self.display(self.root, Side::Up, &mut v, f);
           Ok(())
       }
   }

}

/// Decodes and prints a previously generated tree. fn main() {

   let encoded = r#"{"root":0,"store":[{"key":0,"value":0.45,"left":1,"right":3,
       "up":null},{"key":-8,"value":-0.94,"left":7,"right":2,"up":0}, {"key":-1,
       "value":0.15,"left":8,"right":null,"up":1},{"key":7, "value":-0.29,"left":4,
       "right":9,"up":0},{"key":5,"value":0.80,"left":5,"right":null,"up":3},
       {"key":4,"value":-0.85,"left":6,"right":null,"up":4},{"key":3,"value":-0.46,
       "left":null,"right":null,"up":5},{"key":-10,"value":-0.85,"left":null,
       "right":13,"up":1},{"key":-6,"value":-0.42,"left":null,"right":10,"up":2},
       {"key":9,"value":0.63,"left":12,"right":null,"up":3},{"key":-3,"value":-0.83,
       "left":null,"right":11,"up":8},{"key":-2,"value":0.75,"left":null,"right":null,
       "up":10},{"key":8,"value":-0.48,"left":null,"right":null,"up":9},{"key":-9,
       "value":0.53,"left":null,"right":null,"up":7}]}"#;
   let tree: Tree<i32, f32> = json::decode(&encoded).unwrap();
   println!("{}", tree);

} </lang>

Output:

Sidef

Translation of: Raku

<lang ruby>func visualize_tree(tree, label, children,

                   indent = ,
                   mids = ['├─', '│ '],
                   ends = ['└─', '  '],

) {

   func visit(node, pre) {
       gather {
           take(pre[0] + label(node))
           var chldn = children(node)
           var end = chldn.end
           chldn.each_kv { |i, child|
               if (i == end) { take(visit(child, [pre[1]] ~X+ ends)) }
               else          { take(visit(child, [pre[1]] ~X+ mids)) }
           }
       }
   }
   visit(tree, [indent] * 2)

}

var tree = 'root':['a':['a1':['a11':[]]],'b':['b1':['b11':[]],'b2':[],'b3':[]]] say visualize_tree(tree, { .first }, { .second }).flatten.join("\n")</lang>

Output:

root
├─a
│ └─a1
│   └─a11
└─b
  ├─b1
  │ └─b11
  ├─b2
  └─b3

Tcl

Library: Tcllib (Package: struct::tree)

<lang tcl>package require struct::tree

proc visualize_tree {tree {nameattr name}} {

   set path {}
   $tree walk [$tree rootname] -order both {mode node} {

if {$mode eq "enter"} { set s "" foreach p $path { append s [expr {[$tree next $p] eq "" ? " " : "\u2502 "}] } lappend path $node append s [expr { [$tree next $node] eq "" ? "\u2514\u2500" : "\u251c\u2500" }] if {[$tree keyexists $node $nameattr]} { set name [$tree get $node $nameattr] } else { # No node name attribute; use the raw name set name $node } puts "$s$name" } else { set path [lrange $path 0 end-1] }

}</lang> Demonstrating: <lang tcl># Sample tree to demonstrate with struct::tree t deserialize {root {} {} a 0 {} d 3 {} e 3 {} f 9 {} b 0 {} c 0 {}} visualize_tree t</lang>

Output:

└─root
  ├─a
  │ ├─d
  │ └─e
  │   └─f
  ├─b
  └─c

Wren

Translation of: C

Library: Wren-dynamic

<lang ecmascript>import "/dynamic" for Struct import "random" for Random

var Stem = Struct.create("Stem", ["str", "next"])

var SDOWN = " |" var SLAST = " `" var SNONE = " "

var rand = Random.new()

var tree // recursive tree = Fn.new { |root, head|

   var col = Stem.new(null, null)
   var tail = head
   while (tail) {
       System.write(tail.str)
       if (!tail.next) break
       tail = tail.next
   }
   System.print("--%(root)")
   if (root <= 1) return
   if (tail && tail.str == SLAST) tail.str = SNONE
   if (!tail) {
       tail = head = col
   } else {
       tail.next = col
   }
   while (root != 0) { // make a tree by doing something random
       var r = 1 + rand.int(root)
       root = root - r
       col.str = (root != 0) ? SDOWN : SLAST
       tree.call(r, head)
   }
   tail.next = null

}

var n = 8 tree.call(n, null)</lang>

Output:

Sample output:

--8
  |--7
  |  |--6
  |  |  |--4
  |  |  |  |--1
  |  |  |  `--3
  |  |  |     |--1
  |  |  |     `--2
  |  |  |        |--1
  |  |  |        `--1
  |  |  `--2
  |  |     `--2
  |  |        |--1
  |  |        `--1
  |  `--1
  `--1

Yabasic

<lang Yabasic>clear screen

dim colore$(1)

maxCol = token("white yellow cyan green red", colore$())

showTree(0, "[1[2[3][4[5][6]][7]][8[9]]]") print "\n\n\n" showTree(0, "[1[2[3[4]]][5[6][7[8][9]]]]")

sub showTree(n, A$)

   local i, c$
   static co
   
   c$ = left$(A$, 1)
   
   if c$ = "" return
   
   switch c$
   case "[":   co = co + 1 : showTree(n + 1, right$(A$, len(A$) - 1))
               break
   case "]":   co = co - 1 : showTree(n - 1, right$(A$, len(A$) - 1))
               break
   default:    for i = 2 to n
                   print "  ";
               next i
               co = max(min(co, maxCol), 1)
               print color(colore$(co)) "\xc0-", c$
               showTree(n, right$(A$, len(A$) - 1))
               break
   end switch

end sub </lang>

zkl

In zkl, the Vault is a global object store object (aka thread safe dictionary). Basically a tiny file system for objects. It has a "dir" method to display the contents

Output:

:Vault.dir()
...
Compiler
   Asm
   Compiler
Dictionary
Exception
Test
   UnitTester
   foo
      bar
...

It does this with data that looks like: L("Network.TCPServerSocket","File","ZKLShell.Granny","Int","startup","Utils.Inspector","Thread.Straw","Ref","Utils.Argh" ...) <lang zkl>fcn vaultDir(out=Console){

  const INDENT="   ";
  space:=""; lastPath:=L();
  foreach fullname in (TheVault.BaseClass.contents.sort()){
     path:=fullname.split("."); name:=path.pop();
     if(lastPath==path) out.writeln(space,name);
     else{

n:=0; p:=path.copy(); try{ while(path[0]==lastPath[0]) { n+=1; path.pop(0); lastPath.pop(0); } }catch{} space=INDENT*n; foreach dir in (path){ out.writeln(space,dir); space+=INDENT; } out.writeln(space,name); lastPath=p;

     }
  }
  ""	// so startup has something to display

} </lang>

PHP

<lang PHP> <?php

function printTree( array $tree , string $key = "." , string $stack = "" , $first = TRUE , $firstPadding = NULL ) {

   if ( gettype($tree) == "array" )
   {
       if($firstPadding === NULL) $firstPadding = ( count($tree)>1 ) ? "│   " : "    " ;
       echo   $key . PHP_EOL ;
       foreach ($tree as $key => $value) {
           if ($key === array_key_last($tree)){
               echo (($first) ? "" : $firstPadding ) . $stack . "└── ";
               $padding = "    ";
               if($first) $firstPadding = "    ";
           }
           else {
               echo (($first) ? "" : $firstPadding ) . $stack . "├── ";
               $padding = "│   ";
           }
           if( is_array($value) )printTree( $value , $key ,   $stack . (($first) ? "" : $padding ) , FALSE , $firstPadding );
           else echo $key . " -> " . $value . PHP_EOL;
       }
   }
   else echo $tree . PHP_EOL;

}

// ---------------------------------------TESTING FUNCTION-------------------------------------

$sample_array_1 = [

   0 => [
       'item_id' => 6,
       'price' => "2311.00",
       'qty' => 12,
       'discount' => 0
   ],
   1 => [
       'item_id' => 7,
       'price' => "1231.00",
       'qty' => 1,
       'discount' => 12
   ],
   2 => [
       'item_id' => 8,
       'price' => "123896.00",
       'qty' => 0,
       'discount' => 24
   ]

]; $sample_array_2 = array(

   array(
        "name"=>"John",
       "lastname"=>"Doe",
       "country"=>"Japan",
       "nationality"=>"Japanese",
       "job"=>"web developer",
       "hobbies"=>array(
               "sports"=>"soccer",
               "others"=>array(
                       "freetime"=>"watching Tv"
               )
       )

); $sample_array_3 = [

   "root" => [
       "first_depth_node1" =>[
           "second_depth_node1",
           "second_depth_node2" => [
               "third_depth_node1" ,
               "third_depth_node2" ,
               "third_depth_node3" => [
                   "fourth_depth_node1",
                   "fourth_depth_node2",
               ]
               ],
           "second_depth_node3",
       ] ,
       "first_depth_node2" => [
           "second_depth_node4" => [ "third_depth_node3" => [1]]
       ]
       ]

]; $sample_array_4 = []; $sample_array_5 = ["1"]; $sample_array_5 = ["1"]; $sample_array_6 = [

   "T",
   "Ta",
   "Tad",
   "Tada",
   "Tadav",
   "Tadavo",
   "Tadavom",
   "Tadavomn",
   "Tadavomni",
   "Tadavomnis",
   "TadavomnisT",

];

printTree($sample_array_1); echo PHP_EOL . "------------------------------" . PHP_EOL; printTree($sample_array_2); echo PHP_EOL . "------------------------------" . PHP_EOL; printTree($sample_array_3); echo PHP_EOL . "------------------------------" . PHP_EOL; printTree($sample_array_4); echo PHP_EOL . "------------------------------" . PHP_EOL; printTree($sample_array_5); echo PHP_EOL . "------------------------------" . PHP_EOL; printTree($sample_array_6);

?> </lang>

Output:

.
├── 0
│   ├── item_id -> 6
│   ├── price -> 2311.00
│   ├── qty -> 12
│   └── discount -> 0
├── 1
│   ├── item_id -> 7
│   ├── price -> 1231.00
│   ├── qty -> 1
│   └── discount -> 12
└── 2
    ├── item_id -> 8
    ├── price -> 123896.00
    ├── qty -> 0
    └── discount -> 24

------------------------------
.
└── 0
    ├── name -> John
    ├── lastname -> Doe
    ├── country -> Japan
    ├── nationality -> Japanese
    ├── job -> web developer
    └── hobbies
        ├── sports -> soccer
        └── others
            └── freetime -> watching Tv

------------------------------
.
└── root
    ├── first_depth_node1
    │   ├── 0 -> second_depth_node1
    │   ├── second_depth_node2
    │   │   ├── 0 -> third_depth_node1
    │   │   ├── 1 -> third_depth_node2
    │   │   └── third_depth_node3
    │   │       ├── 0 -> fourth_depth_node1
    │   │       └── 1 -> fourth_depth_node2
    │   └── 1 -> second_depth_node3
    └── first_depth_node2
        └── second_depth_node4
            └── third_depth_node3
                └── 0 -> 1

------------------------------
.

------------------------------
.
└── 0 -> 1

------------------------------
.
├── 0 -> T
├── 1 -> Ta
├── 2 -> Tad
├── 3 -> Tada
├── 4 -> Tadav
├── 5 -> Tadavo
├── 6 -> Tadavom
├── 7 -> Tadavomn
├── 8 -> Tadavomni
├── 9 -> Tadavomnis
└── 10 -> TadavomnisT